beets-alternatives: Add myself as maintainer

I've introduced the plugin and have been maintaining it ever since, so
it's time to make myself the official maintainer in order to avoid
confusion about who to address when issues about the alternatives plugin
arise.

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @wisp3rwind

pkgs/tools/audio/beets/alternatives-plugin.nix

@@ -19,6 +19,7 @@ pythonPackages.buildPythonApplication rec {
   meta = {
     description = "Beets plugin to manage external files";
     homepage = https://github.com/geigerzaehler/beets-alternatives;
+    maintainers = [ stdenv.lib.maintainers.aszlig ];
     license = stdenv.lib.licenses.mit;
   };
 }