[librest: 2/3] Update readme: add RestDemo flatpak build instructions

[Günther Wagner <gwagner src gnome org>]

commit 0f273070addaed4f215641a7a37bcce94d4496bb
Author: baarkerlounger <db slothlife xyz>
Date:   Wed Jan 19 10:45:20 2022 +0000

    Update readme: add RestDemo flatpak build instructions

 README | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)
---
diff --git a/README b/README
index d73dc25..6d6c098 100644
--- a/README
+++ b/README
@@ -43,6 +43,30 @@ siblings for the nodes of the same type that share the same parent. This makes
 it easy for instance to get a list of all the "photo" nodes in a document from
 the root.
 
+Demo application
+~~~~~~~~~~~~~~~~~~~
+
+A small Postman clone is provided in `examples/demo` to test the requests librest
+is making. Flatpak is the recommended way of building and installing it:
+
+```
+# Add Flathub and the gnome-nightly repo
+flatpak remote-add --user --if-not-exists flathub https://dl.flathub.org/repo/flathub.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 org.gnome.Platform
+```
+
+**Inside** the `examples/demo` folder run:
+```
+flatpak-builder --user --install app org.gnome.Librest.json
+```
+Run the application
+```
+flatpak run org.gnome.RestDemo
+```
+
 [1] - http://en.wikipedia.org/wiki/Representational_State_Transfer
 [2] - http://live.gnome.org/LibSoup
 [3] - http://xmlsoft.org/