improve instructions for setting admin credentials in manifest
improve instructions for setting admin credentials in manifest

cloudfoundry/cf-riak-cs-release,mikfreedman/cf-riak-cs-release,mikfreedman/cf-riak-cs-release,cloudfoundry/cf-riak-cs-release,cloudfoundry/cf-riak-cs-release,cloudfoundry/cf-riak-cs-release,datianshi/cf-riak-cs-release,mikfreedman/cf-riak-cs-release,datianshi/cf-riak-cs-release,datianshi/cf-riak-cs-release,mikfreedman/cf-riak-cs-release,datianshi/cf-riak-cs-release