suggest `*.desktop` for AppImage (#10823)

Co-authored-by: Michael Davis <mcarsondavis@gmail.com>

book/src/package-managers.md

@@ -102,6 +102,14 @@ chmod +x helix-*.AppImage # change permission for executable mode
 ./helix-*.AppImage # run helix
 ```
 
+You can optionally [add the `.desktop` file](./building-from-source.md#configure-the-desktop-shortcut). Helix must be installed in `PATH` with the name `hx`. For example:
+```sh
+mkdir -p "$HOME/.local/bin"
+mv helix-*.AppImage "$HOME/.local/bin/hx"
+```
+
+and make sure `~/.local/bin` is in your `PATH`.
+
 ## macOS
 
 ### Homebrew Core