Add note on how to publish mvn snapshot for hadoop1 and hadoop2

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1490467 13f79535-47bb-0310-9956-ffa450edef68
Added hackathon notice

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1490511 13f79535-47bb-0310-9956-ffa450edef68