banshee: add homepage

pkgs/applications/audio/banshee/default.nix

···
         -i $out/bin/banshee
   '';
   meta = with lib; {
+    homepage = "http://banshee.fm/";
     description = "A music player written in C# using GNOME technologies";
     platforms = platforms.linux;
     maintainers = [ maintainers.zohl ];