mpris-scrobbler: add ListenBrainz to the desc.

The project’s online manpage (https://www.mankier.com/1/mpris-scrobbler)
mentions ListenBrainz before the other services.

pkgs/tools/audio/mpris-scrobbler/default.nix

···
   };
 
   meta = with lib; {
-    description = "Minimalistic scrobbler for libre.fm & last.fm";
+    description = "Minimalistic scrobbler for ListenBrainz, libre.fm, & last.fm";
     homepage = "https://github.com/mariusor/mpris-scrobbler";
     license = licenses.mit;
     maintainers = with maintainers; [ emantor ];