feat(publishing): add support for prebuilt AppImage package

This update enhances the publishing workflow by introducing a new
prebuilt AppImage package for Gitty, allowing users to install
the application without needing to compile from source. The
workflow now includes steps to generate and publish the binary
AUR package alongside the standard source package.

- Introduced PKGBUILD-bin for the prebuilt AppImage
- Updated workflow to handle both source and binary package publishing
- Enhanced README to guide users on installing the new package

README.md

@@ -60,6 +60,12 @@ Install Gitty from the AUR with an AUR helper:
 yay -S gitty-desktop
 ```
 
+To install the prebuilt AppImage instead of compiling from source:
+
+```bash
+yay -S gitty-desktop-bin
+```
+
 Or build the AUR package manually:
 
 ```bash
@@ -68,8 +74,9 @@ cd gitty-desktop
 makepkg -si
 ```
 
-The AUR recipe downloads the public Gitea release archive and builds Gitty from
-source. The release pipeline updates its version, checksum, and `.SRCINFO`.
+The source recipe downloads the public Gitea release archive and builds Gitty.
+The `-bin` recipe installs the prebuilt AppImage. The release pipeline updates
+both packages' versions, checksums, and `.SRCINFO` files.
 
 ---