Add version requirement for bs1770gain to the documentation
Add version requirement for bs1770gain to the documentation

shamangeorge/beets,beetbox/beets,sampsyo/beets,jackwilsdon/beets,shamangeorge/beets,sampsyo/beets,ibmibmibm/beets,shamangeorge/beets,sampsyo/beets,SusannaMaria/beets,jackwilsdon/beets,beetbox/beets,ibmibmibm/beets,SusannaMaria/beets,jackwilsdon/beets,SusannaMaria/beets,beetbox/beets,sampsyo/beets,shamangeorge/beets,ibmibmibm/beets,beetbox/beets,ibmibmibm/beets,jackwilsdon/beets,SusannaMaria/beets