[libadwaita] Use title case for titles in Markdown files

[Alexander Mikhaylenko <alexm src gnome org>]

commit 11f49c654b2a11e29ea88894d9a47e62553e3918
Author: Adrien Plazas <kekun plazas laposte net>
Date:   Tue May 25 13:47:50 2021 +0200

    Use title case for titles in Markdown files

 .gitlab-ci/README.md     |  2 +-
 HACKING.md               | 14 +++++++-------
 README.md                |  2 +-
 src/stylesheet/README.md |  4 ++--
 4 files changed, 11 insertions(+), 11 deletions(-)
---
diff --git a/.gitlab-ci/README.md b/.gitlab-ci/README.md
index c21f2895..82b3c1fe 100644
--- a/.gitlab-ci/README.md
+++ b/.gitlab-ci/README.md
@@ -1,4 +1,4 @@
-### Checklist for Updating the Docker images
+### Checklist for Updating the Docker Images
 
  - [ ] Update the `${image}.Dockerfile` file with the dependencies
  - [ ] Run `./run-docker.sh build --base ${image} --version ${number}`
diff --git a/HACKING.md b/HACKING.md
index 4de662f7..152fcddc 100644
--- a/HACKING.md
+++ b/HACKING.md
@@ -2,7 +2,7 @@ Building
 ========
 For build instructions see the README.md
 
-Pull requests
+Pull Requests
 =============
 Before filing a pull request run the tests:
 
@@ -27,7 +27,7 @@ We mostly use kernel style but
 * Use spaces, never tabs
 * Use 2 spaces for indentation
 
-GTK style function argument indentation
+GTK Style Function Argument Indentation
 ----------------------------------------
 Use GTK style function argument indentation. It's harder for renames but it's
 what GNOME upstream projects do.
@@ -199,7 +199,7 @@ enum {
 Also note that the last element ends with a comma to reduce diff noise when
 adding further properties.
 
-Comment style
+Comment Style
 -------------
 In comments use full sentences with proper capitalization and punctuation.
 
@@ -233,7 +233,7 @@ g_signal_connect(self, "clicked", G_CALLBACK (handle_button_clicked), NULL);
 ```
 
 
-Static functions
+Static Functions
 ----------------
 Static functions don't need the class prefix.  E.g. with a type foo_bar:
 
@@ -261,7 +261,7 @@ These functions are usually never called directly but only assigned once in
 *<class_name>_constructed* so the longer name is kind of acceptable. This also
 helps to distinguish virtual methods from regular private methods.
 
-Self argument
+Self Argument
 -------------
 The first argument is usually the object itself so call it *self*. E.g. for a
 non public function:
@@ -293,7 +293,7 @@ foo_button_get_state (FooButton *self)
 }
 ```
 
-User interface files
+User Interface Files
 --------------------
 User interface files should end in *.ui*. If there are multiple ui
 files put them in a ui/ subdirectory below the sources
@@ -314,7 +314,7 @@ Use minus signs instead of underscores in property names:
 <property name="margin_start">12</property>
 ```
 
-Automatic cleanup
+Automatic Cleanup
 -----------------
 It's recommended to use `g_auto()`, `g_autoptr()`, `g_autofree()` for
 automatic resource cleanup when possible.
diff --git a/README.md b/README.md
index 8016394e..c66a811a 100644
--- a/README.md
+++ b/README.md
@@ -37,6 +37,6 @@ _build/run _build/examples/adwaita-1-demo
 The documentation can be found online
 [here](https://gnome.pages.gitlab.gnome.org/libadwaita/doc/).
 
-## Getting in touch
+## Getting in Touch
 
 Matrix room: [#libadwaita:gnome.org](https://matrix.to/#/#libadwaita:gnome.org)
diff --git a/src/stylesheet/README.md b/src/stylesheet/README.md
index 64bba1ae..53917ba6 100644
--- a/src/stylesheet/README.md
+++ b/src/stylesheet/README.md
@@ -6,7 +6,7 @@ Summary
 * Note that meson always builds out-of-tree, so the modified css files will
   appear in your builddir.
 
-Theme variants
+Theme Variants
 --------------
 
 The Adwaita theme comes in 4 variants: light, dark, hc (highcontrast) and
@@ -14,7 +14,7 @@ hc-dark (highcontrast inverse). The generated CSS files for the variants
 are called Adwaita-$variant.css. For technical reasons, GTK adds one level
 of include wrappers around these, which are called gtk-$variant.css.
 
-How to tweak the theme
+How to Tweak the Theme
 ----------------------
 
 Adwaita is a complex theme, so to keep it maintainable it's written and