fix: correct hyperhive.user.gid description — gid works independently of uid

nix/templates/harness-base.nix

@@ -164,10 +164,9 @@ in
     example = 1100;
     description = ''
       Optional fixed GID for the per-agent unix group. `null` (default)
-      lets NixOS auto-assign. When `uid` is set, setting `gid` to the
-      same value keeps uid == gid (the conventional Unix pattern for
-      per-user groups). Has no effect unless also setting
-      `hyperhive.user.uid`.
+      lets NixOS auto-assign. Usually set alongside `hyperhive.user.uid`
+      to the same value (the conventional Unix pattern for per-user
+      groups where uid == gid), but can be set independently.
     '';
   };