regreet: add update script

pkgs/by-name/re/regreet/package.nix

@@ -8,6 +8,7 @@
   gtk4,
   pango,
   librsvg,
+  nix-update-script,
 }:
 
 rustPlatform.buildRustPackage (finalAttrs: {
@@ -36,6 +37,8 @@ rustPlatform.buildRustPackage (finalAttrs: {
     librsvg
   ];
 
+  passthru.updateScript = nix-update-script { };
+
   meta = {
     description = "Clean and customizable greeter for greetd";
     homepage = "https://github.com/rharish101/ReGreet";