docs: RygelMediaEngine: Suggest transcoder implementation.
docs: RygelMediaEngine: Suggest transcoder implementation.

Added some text from Mark Ryan.

Pelagicore/Media-Manager-Rygel-patched,jku/rygel,Tarnyko/rygel,Tarnyko/rygel,GNOME/rygel,GNOME/rygel,jku/rygel,GNOME/rygel,Pelagicore/Media-Manager-Rygel-patched,Pelagicore/Media-Manager-Rygel-patched