Link to tutorial for creating desktop files

Guides/os.md

@@ -46,6 +46,8 @@ FTL and Into the Breach saves are in `.local/share/` folder.
 
 Set your _desktop_ file in `~/.local/share/applications/`.
 
+[Tutorial to create a desktop file](https://linuxconfig.org/how-to-create-custom-desktop-files-for-launchers-on-linux).
+
 ## Grub
 
 `sudo update-grub`