MB-12274: Update READMEs for 2.5.2

Change-Id: I4468fbd0b1cf0b0ee58f6bc7dcf7e4b3c4d7a7ef
Reviewed-on: http://review.couchbase.org/43352
Reviewed-by: Chris Hillery <ceej@couchbase.com>
Tested-by: Chris Hillery <ceej@couchbase.com>