docs: Update for switch to fd.o 22.08 runtime

Part-of: <https://gitlab.gnome.org/GNOME/fractal/-/merge_requests/1144>

CONTRIBUTING.md

@@ -29,18 +29,18 @@ If you're building Fractal with Flatpak (via GNOME Builder or the command line),
 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
+# Add Flathub and the gnome-nightly repo
+flatpak remote-add --user --if-not-exists flathub https://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//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 rust-stable extension from Flathub
+flatpak install --user flathub org.freedesktop.Sdk.Extension.rust-stable//22.08
 
-# Install the required llvm extension from Flathub-beta
-flatpak install --user flathub-beta org.freedesktop.Sdk.Extension.llvm14//22.08beta
+# Install the required llvm extension from Flathub
+flatpak install --user flathub org.freedesktop.Sdk.Extension.llvm14//22.08
 ```
 
 ### GNOME Builder

README.md

@@ -49,8 +49,7 @@ If you want to try Fractal Next without building it yourself, it is available as
 in the gnome-nightly repo.
 
 ```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
+# Add the gnome-nightly repo
 flatpak remote-add --user --if-not-exists gnome-nightly https://nightly.gnome.org/gnome-nightly.flatpakrepo
 
 # Install the nightly build