Update documentations for LIBEVENT_THREAD
Update documentations for LIBEVENT_THREAD

Change-Id: Ib209a70cbce6ddadfd7013a94de468d565d39376
Reviewed-on: http://review.couchbase.org/87663
Reviewed-by: Tim Bradgate <f1a26ee65f021cb7d82b83dfb09abf144d3eb64f@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine