HBASE-7834. Document Hadoop version support matrix in the book

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1446379 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'trunk' of https://github.com/apache/hbase into clean
Merge branch 'clean' into fw_client