Document workaround for missing readline on OSX 10.11 (#3599)
Document workaround for missing readline on OSX 10.11 (#3599)

Signed-off-by: Ben Christel <1e6f33b93edb5b67641d5788dfa53877a58fab99@pivotal.io>
ashwinstar/gpdb,Chibin/gpdb,jmcatamney/gpdb,adam8157/gpdb,xinzweb/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,xinzweb/gpdb,edespino/gpdb,50wu/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,adam8157/gpdb,ashwinstar/gpdb,xinzweb/gpdb,Chibin/gpdb,jmcatamney/gpdb,edespino/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,xinzweb/gpdb,xinzweb/gpdb,adam8157/gpdb,Chibin/gpdb,jmcatamney/gpdb,xinzweb/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,Chibin/gpdb,ashwinstar/gpdb,edespino/gpdb,adam8157/gpdb,50wu/gpdb,edespino/gpdb,adam8157/gpdb,Chibin/gpdb,adam8157/gpdb,edespino/gpdb,Chibin/gpdb,edespino/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,lisakowen/gpdb,lisakowen/gpdb,yuanzhao/gpdb,50wu/gpdb,edespino/gpdb,jmcatamney/gpdb,xinzweb/gpdb,jmcatamney/gpdb,50wu/gpdb,yuanzhao/gpdb,edespino/gpdb,50wu/gpdb,Chibin/gpdb,edespino/gpdb,yuanzhao/gpdb,lisakowen/gpdb,lisakowen/gpdb,greenplum-db/gpdb,lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,lisakowen/gpdb,Chibin/gpdb,Chibin/gpdb,50wu/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,50wu/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,Chibin/gpdb,lisakowen/gpdb,edespino/gpdb,xinzweb/gpdb,yuanzhao/gpdb,adam8157/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,adam8157/gpdb,50wu/gpdb