[fractal] docs: Move build instructions and improve contributing guidelines

[Marge Bot <marge-bot src gnome org>]

commit 489f297fbd3523985861d42ea65bb9b0918f4471
Author: Kévin Commaille <zecakeh tedomum fr>
Date:   Mon Aug 29 11:18:28 2022 +0200

    docs: Move build instructions and improve contributing guidelines
    
    Co-authored-by: Alexandre Franke <afranke gnome org>
    Part-of: <https://gitlab.gnome.org/GNOME/fractal/-/merge_requests/1140>

 CONTRIBUTING.md | 163 ++++++++++++++++++++++++++++++++++++++++++++++++++++----
 README.md       |  70 +++---------------------
 2 files changed, 162 insertions(+), 71 deletions(-)
---
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 722e9d60d..0868c108f 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -1,20 +1,165 @@
 # Contributing
 
-## Workflow
+## Newcomers
 
 [Fractal](https://gitlab.gnome.org/GNOME/fractal/) follows the [GNOME Newcomers 
workflow](https://wiki.gnome.org/Newcomers/).
 Follow these pages to learn how to contribute.
 
-We only support building with [flatpak](https://flatpak.org/) using [GNOME 
Builder](https://wiki.gnome.org/Apps/Builder).
-If you insist on using any other method, they may work, but you will be on your own.
+Here are also a few links to help you get started with Rust and the GTK Rust bindings:
 
-You will need to manually install the latest version of the Rust extension of the FreeDesktop SDK.
-To do this, just run `flatpak install --user org.freedesktop.Sdk.Extension.rust-stable//21.08`
+- [Learn Rust](https://www.rust-lang.org/learn)
+- [GUI development with Rust and GTK 4](https://gtk-rs.org/gtk4-rs/stable/latest/book)
+- [gtk-rs website](https://gtk-rs.org/)
 
-## Merge requests
+[The Rust docs of our application](https://gnome.pages.gitlab.gnome.org/fractal/) might also be
+useful.
 
-We expect all code contributions to be correctly formatted.
-Before submitting a merge request, please run `cargo fmt` on your branch to ensure this is the case.
-It is also recommended to run `cargo clippy` as that will catch common errors and improve the quality of 
your submissions.
+Don't hesitate to join [our Matrix room](https://matrix.to/#/#fractal:gnome.org) to come talk to us
+and ask us any questions you might have.
+
+## Build Instructions
+
+### Prerequisites
+
+Fractal is written in Rust, so you will need to have at least Rust 1.60 and Cargo available on your
+system. You will also need to install the Rust nightly toolchain to be able to run our
+[pre-commit hook](#pre-commit).
+
+If you're building Fractal with Flatpak (via GNOME Builder or the command line), you will need to
+manually add the necessary remotes and install the required FreeDesktop extensions:
+
+```sh
+# Add Flathub-beta and the gnome-nightly repo
+flatpak remote-add --user --if-not-exists flathub-beta https://flathub.org/beta-repo/flathub-beta.flatpakrepo
+flatpak remote-add --user --if-not-exists gnome-nightly https://nightly.gnome.org/gnome-nightly.flatpakrepo
+
+# Install the gnome-nightly Sdk and Platform runtime
+flatpak install --user gnome-nightly org.gnome.Sdk//master org.gnome.Platform//master
+
+# Install the required rust-stable extension from Flathub-beta
+flatpak install --user flathub-beta org.freedesktop.Sdk.Extension.rust-stable//22.08beta
+
+# Install the required llvm extension from Flathub-beta
+flatpak install --user flathub-beta org.freedesktop.Sdk.Extension.llvm14//22.08beta
+```
+
+### GNOME Builder
+
+Using [GNOME Builder](https://wiki.gnome.org/Apps/Builder) with [flatpak](https://flatpak.org/) is
+the recommended way of building and installing Fractal.
+
+By default, GNOME Builder should select the `org.gnome.Fractal.Devel.json` manifest, which is the
+manifest used for building the nightly version. It is recommended to switch to the
+`org.gnome.Fractal.Hack.json` manifest which will build much faster.
+
+### Flatpak via fenv
+
+As an alternative, [fenv](https://gitlab.gnome.org/ZanderBrown/fenv) allows to setup a flatpak
+environment from the command line and execute commands in that environment.
+
+First, install fenv:
+
+```sh
+# Clone the project somewhere on your system
+git clone https://gitlab.gnome.org/ZanderBrown/fenv.git
+
+# Move into the folder
+cd fenv
+
+# Install fenv with Cargo
+cargo install --path .
+```
+
+You can now discard the `fenv` directory if you want.
+
+After that, move into the directory where you cloned Fractal and setup the project:
+
+```sh
+# Setup the flatpak environment
+fenv gen build-aux/org.gnome.Fractal.Hack.json
+
+# Initialize the build system
+fenv exec -- meson --prefix=/app _build
+```
+
+Finally, build and run the application:
+
+```sh
+# Build the project
+fenv exec -- ninja -C _build
+
+# Install the application in the flatpak environment
+fenv exec -- ninja -C _build install
+
+# Launch Fractal
+fenv exec ./_build/src/fractal
+```
+
+To test changes you make to the code, re-run these three last commands.
+
+### Install the flatpak
+
+Some features that interact with the system require the app to be installed to test them (i.e.
+notifications, command line arguments, etc.).
+
+Move inside the `build-aux` folder and then build and install the app:
+
+```sh
+cd build-aux
+flatpak-builder --user --install app org.gnome.Fractal.Hack.json
+```
+
+It can then be entirely removed from your system with:
+
+```sh
+flatpak remove --delete-data org.gnome.Fractal.Hack
+```
+
+### GNU/Linux
+
+If you decide to ignore our recommendation and build on your host system, outside of Flatpak, you
+will need Meson and Ninja.
+
+```sh
+meson . _build --prefix=/usr/local
+ninja -C _build
+sudo ninja -C _build install
+```
+
+## Pre-commit
+
+We expect all code contributions to be correctly formatted. To help with that, a pre-commit hook
+should get installed as part of the building process. It runs the `scripts/checks.sh` script. It's a
+quick script that makes sure that the code is correctly formatted with `rustfmt`, among other
+things. Make sure that this script is effectively run before submitting your merge request,
+otherwise CI will probably fail right away.
+
+You should also run `cargo clippy` as that will catch common errors and improve the quality of your
+submissions and is once again checked by our CI.
+
+## Commit
 
 Please follow the [GNOME commit message guidelines](https://wiki.gnome.org/Git/CommitMessages).
+
+## Merge Request
+
+Before submitting a merge request, make sure that [your fork is available 
publicly](https://gitlab.gnome.org/help/user/public_access.md),
+otherwise CI won't be able to run.
+
+Use the title of your commit as the title of your MR if there's only one. Otherwise it should
+summarize all your commits. If your commits do several tasks that can be separated, open several
+merge requests.
+
+In the details, write a more detailed description of what it does. If your changes include a change
+in the UI or the UX, provide screenshots in both light and dark mode, and/or a screencast of the
+new behavior.
+
+Don't forget to mention the issue that this merge request solves or is related to, if applicable.
+GitLab recognizes the syntax `Closes #XXXX` or `Fixes #XXXX` that will close the corresponding
+issue accordingly when your change is merged.
+
+We expect to always work with a clean commit history. When you apply fixes or suggestions,
+[amend](https://git-scm.com/docs/git-commit#Documentation/git-commit.txt---amend) or
+[fixup](https://git-scm.com/docs/git-commit#Documentation/git-commit.txt---fixupamendrewordltcommitgt)
+and [squash](https://git-scm.com/docs/git-rebase#Documentation/git-rebase.txt---autosquash) your
+previous commits that you can then [force 
push](https://git-scm.com/docs/git-push#Documentation/git-push.txt--f).
diff --git a/README.md b/README.md
index 89ef7918c..79b861d2a 100644
--- a/README.md
+++ b/README.md
@@ -57,66 +57,18 @@ flatpak remote-add --user --if-not-exists gnome-nightly https://nightly.gnome.or
 flatpak install --user gnome-nightly org.gnome.Fractal.Devel
 ```
 
-## Build Instructions
+### Runtime Dependencies
 
-### Minimum Rust version
+Fractal doesn't store your **password** but uses [Secret 
Service](https://www.freedesktop.org/wiki/Specifications/secret-storage-spec/)
+to store your other **credentials** so you should have something providing that service on your
+system. If you're using GNOME or KDE this should work for you out of the box with gnome-keyring or
+ksecretservice.
 
-To build Fractal, Rust 1.60 is required. For development, you'll need to install the nightly
-toolchain to be able to run our pre-commit hook that validates the formatting and lints the Rust
-code.
+## Contributing
 
-### Flatpak
+### Code
 
-Flatpak is the recommended way of building and installing Fractal.
-
-First you need to make sure you have the GNOME SDK and Rust toolchain installed.
-
-```sh
-# Add Flathub-beta and the gnome-nightly repo
-flatpak remote-add --user --if-not-exists flathub-beta https://flathub.org/beta-repo/flathub-beta.flatpakrepo
-flatpak remote-add --user --if-not-exists gnome-nightly https://nightly.gnome.org/gnome-nightly.flatpakrepo
-
-# Install the gnome-nightly Sdk and Platform runtime
-flatpak install --user gnome-nightly org.gnome.Sdk//master org.gnome.Platform//master
-
-# Install the required rust-stable extension from Flathub-beta
-flatpak install --user flathub-beta org.freedesktop.Sdk.Extension.rust-stable//22.08beta
-
-# Install the required llvm extension from Flathub-beta
-flatpak install --user flathub-beta org.freedesktop.Sdk.Extension.llvm14//22.08beta
-```
-
-<table><tr><td>
-<p>ℹ️ The instructions below will build the same binary as the one available on the GNOME nightly
-repo. This is an optimised build so it can take a few minutes.</p>
-
-<p>If you're building Fractal for development, use the <code>org.gnome.Fractal.Hack.json</code> manifest
-instead.</p>
-</td></tr></table>
-
-Move inside the `build-aux` folder and then build and install the app:
-
-```sh
-cd build-aux
-flatpak-builder --user --install app org.gnome.Fractal.Devel.json
-```
-
-Fractal Next can then be entirely removed from your system with:
-
-```sh
-flatpak remove --delete-data org.gnome.Fractal.Devel
-```
-
-### GNU/Linux
-
-If you decide to ignore our recommendation and build on your host system,
-outside of Flatpak, you will need Meson and Ninja (as well as Rust and Cargo).
-
-```sh
-meson . _build --prefix=/usr/local
-ninja -C _build
-sudo ninja -C _build install
-```
+Please follow our [contributing guidelines](CONTRIBUTING.md).
 
 ### Translations
 
@@ -124,12 +76,6 @@ Fractal is translated by the GNOME translation team on [Damned lies](https://l10
 
 Find your language in the list on [the Fractal module page on Damned 
lies](https://l10n.gnome.org/module/fractal/).
 
-### Password Storage
-
-Fractal uses [Secret Service](https://www.freedesktop.org/wiki/Specifications/secret-storage-spec/)
-to store the password so you should have something providing that service on your system. If you're
-using GNOME or KDE this should work for you out of the box with gnome-keyring or ksecretservice.
-
 ## Frequently Asked Questions
 
 * Does Fractal have encryption support? Will it ever?