Add some general clarifications to the keydb documentation.
Add some general clarifications to the keydb documentation.

rraptorr/libaacs,ShiftMediaProject/libaacs,mwgoldsmith/aacs,ShiftMediaProject/libaacs,zxlooong/libaacs,zxlooong/libaacs,rraptorr/libaacs,mwgoldsmith/aacs