Readme update with docker quickstart guide (#903)
Readme update with docker quickstart guide (#903)

Added a link to a quickstart docker guide located on the Pivotal Engineering Journal.
Quikling/gpdb,adam8157/gpdb,greenplum-db/gpdb,Chibin/gpdb,cjcjameson/gpdb,0x0FFF/gpdb,edespino/gpdb,adam8157/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,kaknikhil/gpdb,Chibin/gpdb,lisakowen/gpdb,jmcatamney/gpdb,adam8157/gpdb,Quikling/gpdb,janebeckman/gpdb,yuanzhao/gpdb,jmcatamney/gpdb,edespino/gpdb,Quikling/gpdb,Chibin/gpdb,CraigHarris/gpdb,Quikling/gpdb,yuanzhao/gpdb,lintzc/gpdb,royc1/gpdb,lintzc/gpdb,Chibin/gpdb,cjcjameson/gpdb,Chibin/gpdb,cjcjameson/gpdb,kaknikhil/gpdb,CraigHarris/gpdb,Chibin/gpdb,edespino/gpdb,Quikling/gpdb,50wu/gpdb,xuegang/gpdb,edespino/gpdb,rvs/gpdb,yuanzhao/gpdb,lintzc/gpdb,lisakowen/gpdb,royc1/gpdb,rvs/gpdb,Quikling/gpdb,xinzweb/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,0x0FFF/gpdb,jmcatamney/gpdb,royc1/gpdb,royc1/gpdb,CraigHarris/gpdb,kaknikhil/gpdb,rvs/gpdb,xuegang/gpdb,kaknikhil/gpdb,lintzc/gpdb,Quikling/gpdb,lisakowen/gpdb,rvs/gpdb,50wu/gpdb,0x0FFF/gpdb,yuanzhao/gpdb,lisakowen/gpdb,adam8157/gpdb,ashwinstar/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,xuegang/gpdb,cjcjameson/gpdb,kaknikhil/gpdb,royc1/gpdb,kaknikhil/gpdb,xuegang/gpdb,edespino/gpdb,0x0FFF/gpdb,xuegang/gpdb,rvs/gpdb,xinzweb/gpdb,royc1/gpdb,kaknikhil/gpdb,xinzweb/gpdb,CraigHarris/gpdb,adam8157/gpdb,Quikling/gpdb,janebeckman/gpdb,royc1/gpdb,cjcjameson/gpdb,cjcjameson/gpdb,xinzweb/gpdb,ashwinstar/gpdb,lisakowen/gpdb,50wu/gpdb,Quikling/gpdb,greenplum-db/gpdb,Chibin/gpdb,lisakowen/gpdb,50wu/gpdb,lisakowen/gpdb,0x0FFF/gpdb,50wu/gpdb,cjcjameson/gpdb,lintzc/gpdb,yuanzhao/gpdb,0x0FFF/gpdb,ashwinstar/gpdb,adam8157/gpdb,CraigHarris/gpdb,rvs/gpdb,edespino/gpdb,edespino/gpdb,kaknikhil/gpdb,royc1/gpdb,lintzc/gpdb,xuegang/gpdb,50wu/gpdb,xuegang/gpdb,janebeckman/gpdb,janebeckman/gpdb,janebeckman/gpdb,Chibin/gpdb,lintzc/gpdb,CraigHarris/gpdb,lintzc/gpdb,0x0FFF/gpdb,greenplum-db/gpdb,rvs/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,Quikling/gpdb,CraigHarris/gpdb,jmcatamney/gpdb,rvs/gpdb,Chibin/gpdb,janebeckman/gpdb,xinzweb/gpdb,ashwinstar/gpdb,cjcjameson/gpdb,janebeckman/gpdb,janebeckman/gpdb,xinzweb/gpdb,adam8157/gpdb,yuanzhao/gpdb,lisakowen/gpdb,Chibin/gpdb,edespino/gpdb,xuegang/gpdb,50wu/gpdb,ashwinstar/gpdb,kaknikhil/gpdb,yuanzhao/gpdb,lintzc/gpdb,kaknikhil/gpdb,greenplum-db/gpdb,CraigHarris/gpdb,edespino/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,50wu/gpdb,rvs/gpdb,janebeckman/gpdb,janebeckman/gpdb,adam8157/gpdb,xinzweb/gpdb,rvs/gpdb,yuanzhao/gpdb,cjcjameson/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,edespino/gpdb,0x0FFF/gpdb,xuegang/gpdb,CraigHarris/gpdb,jmcatamney/gpdb,xinzweb/gpdb