PCBC-174: Add documentation of the Couchbase class

Change-Id: Id02e5da01ab43204d957e3df1899bdd364698f6a
Reviewed-on: http://review.couchbase.org/23641
Reviewed-by: Matt Ingenthron <matt@couchbase.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>