rtkit: add update script

pkgs/by-name/rt/rtkit/package.nix

@@ -11,6 +11,7 @@
   polkit,
   systemd,
   fetchpatch,
+  nix-update-script,
 }:
 
 stdenv.mkDerivation (finalAttrs: {
@@ -58,6 +59,8 @@ stdenv.mkDerivation (finalAttrs: {
     (lib.mesonOption "systemd_sysusersdir" "${placeholder "out"}/lib/sysusers.d")
   ];
 
+  passthru.updateScript = nix-update-script { };
+
   meta = {
     homepage = "https://gitlab.freedesktop.org/pipewire/rtkit";
     description = "Daemon that hands out real-time priority to processes";