gain: Add some documentation. Closes T120.
gain: Add some documentation. Closes T120.

HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA,HoerTech-gGmbH/openMHA