MB-8145: added description text for read-only user form

Change-Id: Id67858797019e9a848f5ee1ce133207362b57106
Reviewed-on: http://review.couchbase.org/28081
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>