docs: touchups

docs/getting-started/nix.md

@@ -22,6 +22,7 @@ Using Astal on Nix will require you to package your project.
   in {
     packages.${system}.default = astal.lib.mkLuaPacakge {
       inherit pkgs;
+      src = ./path/to/project; # should contain app.lua
     };
   };
 }