MB-100: Add a note about versioning, tags to deconfuse the situation.

Change-Id: If585bccfe24aa09f4de1779f32185819171b6900
Reviewed-on: http://review.couchbase.org/29306
Reviewed-by: Chiyoung Seo <chiyoung.seo@gmail.com>
Tested-by: Chiyoung Seo <chiyoung.seo@gmail.com>