Update README.md to add the ForestDB paper link and remove the beta link
Update README.md to add the ForestDB paper link and remove the beta link

Change-Id: I9d856f14782fc3d83a198ae4f332eb3640e330bd
Reviewed-on: http://review.couchbase.org/64661
Reviewed-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>
Tested-by: Chiyoung Seo <fcffc23db27b19ee4ebba46695ee6b50e09216a2@couchbase.com>

wurikiji/forestdb,hisundar/forestdb,wurikiji/forestdb,couchbase/forestdb,couchbase/forestdb,hisundar/forestdb