gradle: Update README to highlight workspace and non-workspace plugins
gradle: Update README to highlight workspace and non-workspace plugins

[ci skip]

Closes https://github.com/bndtools/bnd/pull/1371

Signed-off-by: BJ Hargrave <3d26bb3930946e3370762d769a073cece444c2d8@bjhargrave.com>

lostiniceland/bnd,magnet/bnd,magnet/bnd,psoreide/bnd,lostiniceland/bnd,magnet/bnd,mcculls/bnd,mcculls/bnd,psoreide/bnd,mcculls/bnd,lostiniceland/bnd,psoreide/bnd