Add release notes about Search rolling upgrade
Add release notes about Search rolling upgrade

basho/riak,elkingtonmcb/riak,xuejianhai/riak,GabrielNicolasAvellaneda/riak,biddyweb/riak,glickbot/riak,planobe/riak,yangchengjian/riak,planobe/riak,amyvmiwei/riak,laurenrother/riak,authbox-lib/riak,DavidAlphaFox/riak