Add information about the idle timer to the doc
Add information about the idle timer to the doc

Change-Id: Ibf715127e92bedb71c11d629b84ede67942c7782
Reviewed-on: http://review.couchbase.org/60047
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

couchbase/memcached,daverigby/memcached,couchbase/memcached,owendCB/memcached,daverigby/kv_engine,daverigby/memcached,daverigby/kv_engine,daverigby/memcached,daverigby/kv_engine,couchbase/memcached,owendCB/memcached,owendCB/memcached,daverigby/kv_engine,daverigby/memcached,owendCB/memcached,couchbase/memcached