jjui: Add update script using nix-update

pkgs/by-name/jj/jjui/package.nix

@@ -2,6 +2,7 @@
   lib,
   buildGoModule,
   fetchFromGitHub,
+  nix-update-script,
 }:
 buildGoModule {
   pname = "jjui";
@@ -20,6 +21,8 @@ buildGoModule {
     mv $out/bin/cmd $out/bin/jjui
   '';
 
+  passthru.updateScript = nix-update-script { };
+
   meta = {
     description = "A TUI for Jujutsu VCS";
     homepage = "https://github.com/idursun/jjui";