HBASE-8592 [documentation] some updates for the reference guide regarding recent questions on the ML

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1485067 13f79535-47bb-0310-9956-ffa450edef68
HBASE-8591 Doc Improvement: Replication blog

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1485068 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/trunk' into trunk-gd