Update release notes file

Change-Id: I33a8477bf504f9dbf59c92e17aab35e18287e2d4
Reviewed-on: http://review.couchbase.org/30033
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>