mangohud: add update script

pkgs/tools/graphics/mangohud/default.nix

@@ -30,6 +30,7 @@
 , nlohmann_json
 , xorg
 , gamescopeSupport ? true # build mangoapp and mangohudctl
+, nix-update-script
 }:
 
 let
@@ -186,6 +187,8 @@ stdenv.mkDerivation (finalAttrs: {
       --prefix XDG_DATA_DIRS : "$out/share"
   '';
 
+  passthru.updateScript = nix-update-script { };
+
   meta = with lib; {
     description = "A Vulkan and OpenGL overlay for monitoring FPS, temperatures, CPU/GPU load and more";
     homepage = "https://github.com/flightlessmango/MangoHud";