MB-100: Fix the engine name in the readme since we've evolved.

Change-Id: Icdd348f34a85bafaa24c24f18c9370dff3e93fc7
Reviewed-on: http://review.couchbase.org/29305
Reviewed-by: Chiyoung Seo <chiyoung.seo@gmail.com>
Tested-by: Chiyoung Seo <chiyoung.seo@gmail.com>