audio: enable security.rtkit for pipewire

This should avoid stuttering audio when CPU is busy

See: https://nixos.wiki/wiki/PipeWire

modules/audio/default.nix

@@ -54,6 +54,8 @@ in
       };
     };
 
+    # rtkit is optional but recommended
+    security.rtkit.enable = true;
     # Enable sound using pipewire-pulse
     services.pipewire = {
       enable = true;