update description of FlushQueueSize and CompactQueueSize
update description of FlushQueueSize and CompactQueueSize

Change-Id: Idad2f1bb4ba5380db421421aac2b2999faf2ccd1
Reviewed-on: http://review.couchbase.org/c/cbmonitor/+/153391
Tested-by: Bo-Chun Wang <bb86fd206c9c35341feb9b50e74a74a83e254d63@couchbase.com>
Reviewed-by: Bo-Chun Wang <bb86fd206c9c35341feb9b50e74a74a83e254d63@couchbase.com>

couchbase/cbmonitor,couchbase/cbmonitor