audacious: link in Skins from audacious-plugins

pkgs/applications/audio/audacious/default.nix

···
 
   postInstall = lib.optionalString (audacious-plugins != null) ''
     ln -s ${audacious-plugins}/lib/audacious $out/lib
+    ln -s ${audacious-plugins}/share/audacious/Skins $out/share/audacious/
   '';
 
   meta = with lib; {