MB-9475:  2.5 READMEs for macosx

Change-Id: I4656a426e04ba285ec0975e81b96fb95d0a8665f
Reviewed-on: http://review.couchbase.org/32699
Reviewed-by: Philip Labee <philip@couchbase.com>
Reviewed-by: Eric Limare <eric.limare@couchbase.com>
Tested-by: Eric Limare <eric.limare@couchbase.com>