PCBC-181: Update the api-doc for get

Change-Id: I395979ed679d8797d8a20b789ff5d758b15cf749
Reviewed-on: http://review.couchbase.org/24053
Reviewed-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>