readme: link mail lists to the google groups
readme: link mail lists to the google groups

Fixes https://github.com/bndtools/bnd/issues/1871

Signed-off-by: BJ Hargrave<3d26bb3930946e3370762d769a073cece444c2d8@bjhargrave.com>
mcculls/bnd,lostiniceland/bnd,mcculls/bnd,psoreide/bnd,magnet/bnd,lostiniceland/bnd,psoreide/bnd,psoreide/bnd,magnet/bnd,mcculls/bnd,magnet/bnd,lostiniceland/bnd