Update README's install instructions to agree with current reality.
Update README's install instructions to agree with current reality.

zaksoup/gpdb,Quikling/gpdb,yazun/postgres-xl,pavanvd/postgres-xl,ashwinstar/gpdb,yuanzhao/gpdb,kaknikhil/gpdb,postmind-net/postgres-xl,tangp3/gpdb,snaga/postgres-xl,jmcatamney/gpdb,lintzc/gpdb,CraigHarris/gpdb,tangp3/gpdb,janebeckman/gpdb,edespino/gpdb,royc1/gpdb,kaknikhil/gpdb,lintzc/gpdb,edespino/gpdb,Quikling/gpdb,edespino/gpdb,Chibin/gpdb,pavanvd/postgres-xl,arcivanov/postgres-xl,randomtask1155/gpdb,0x0FFF/gpdb,cjcjameson/gpdb,edespino/gpdb,rvs/gpdb,postmind-net/postgres-xl,kaknikhil/gpdb,chrishajas/gpdb,cjcjameson/gpdb,rubikloud/gpdb,ashwinstar/gpdb,techdragon/Postgres-XL,atris/gpdb,techdragon/Postgres-XL,zaksoup/gpdb,CraigHarris/gpdb,lpetrov-pivotal/gpdb,ahachete/gpdb,rvs/gpdb,postmind-net/postgres-xl,lpetrov-pivotal/gpdb,royc1/gpdb,jmcatamney/gpdb,randomtask1155/gpdb,ahachete/gpdb,tpostgres-projects/tPostgres,rubikloud/gpdb,xinzweb/gpdb,pavanvd/postgres-xl,ovr/postgres-xl,zaksoup/gpdb,CraigHarris/gpdb,yuanzhao/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,foyzur/gpdb,foyzur/gpdb,jmcatamney/gpdb,50wu/gpdb,yuanzhao/gpdb,zeroae/postgres-xl,greenplum-db/gpdb,janebeckman/gpdb,atris/gpdb,greenplum-db/gpdb,kaknikhil/gpdb,tpostgres-projects/tPostgres,ashwinstar/gpdb,Chibin/gpdb,chrishajas/gpdb,Chibin/gpdb,lpetrov-pivotal/gpdb,snaga/postgres-xl,foyzur/gpdb,tpostgres-projects/tPostgres,Chibin/gpdb,xuegang/gpdb,yuanzhao/gpdb,janebeckman/gpdb,ahachete/gpdb,oberstet/postgres-xl,oberstet/postgres-xl,rvs/gpdb,janebeckman/gpdb,lpetrov-pivotal/gpdb,foyzur/gpdb,cjcjameson/gpdb,snaga/postgres-xl,0x0FFF/gpdb,foyzur/gpdb,jmcatamney/gpdb,lintzc/gpdb,adam8157/gpdb,xinzweb/gpdb,zaksoup/gpdb,kmjungersen/PostgresXL,0x0FFF/gpdb,kmjungersen/PostgresXL,snaga/postgres-xl,rubikloud/gpdb,postmind-net/postgres-xl,royc1/gpdb,Quikling/gpdb,tangp3/gpdb,foyzur/gpdb,0x0FFF/gpdb,cjcjameson/gpdb,zaksoup/gpdb,royc1/gpdb,ahachete/gpdb,oberstet/postgres-xl,xuegang/gpdb,CraigHarris/gpdb,adam8157/gpdb,oberstet/postgres-xl,arcivanov/postgres-xl,edespino/gpdb,kmjungersen/PostgresXL,rvs/gpdb,xinzweb/gpdb,ovr/postgres-xl,janebeckman/gpdb,CraigHarris/gpdb,cjcjameson/gpdb,randomtask1155/gpdb,cjcjameson/gpdb,randomtask1155/gpdb,yuanzhao/gpdb,yazun/postgres-xl,lisakowen/gpdb,rvs/gpdb,kaknikhil/gpdb,lpetrov-pivotal/gpdb,yuanzhao/gpdb,rvs/gpdb,techdragon/Postgres-XL,CraigHarris/gpdb,lintzc/gpdb,Chibin/gpdb,50wu/gpdb,atris/gpdb,arcivanov/postgres-xl,yazun/postgres-xl,adam8157/gpdb,chrishajas/gpdb,royc1/gpdb,50wu/gpdb,atris/gpdb,edespino/gpdb,greenplum-db/gpdb,Chibin/gpdb,ovr/postgres-xl,CraigHarris/gpdb,pavanvd/postgres-xl,cjcjameson/gpdb,janebeckman/gpdb,arcivanov/postgres-xl,kaknikhil/gpdb,lintzc/gpdb,tangp3/gpdb,xinzweb/gpdb,rvs/gpdb,0x0FFF/gpdb,greenplum-db/gpdb,Postgres-XL/Postgres-XL,pavanvd/postgres-xl,edespino/gpdb,CraigHarris/gpdb,ahachete/gpdb,kmjungersen/PostgresXL,jmcatamney/gpdb,ashwinstar/gpdb,edespino/gpdb,yazun/postgres-xl,royc1/gpdb,lisakowen/gpdb,greenplum-db/gpdb,randomtask1155/gpdb,zeroae/postgres-xl,lisakowen/gpdb,50wu/gpdb,yuanzhao/gpdb,yazun/postgres-xl,rvs/gpdb,xinzweb/gpdb,lintzc/gpdb,adam8157/gpdb,lintzc/gpdb,yuanzhao/gpdb,Quikling/gpdb,Postgres-XL/Postgres-XL,janebeckman/gpdb,lpetrov-pivotal/gpdb,rubikloud/gpdb,atris/gpdb,ashwinstar/gpdb,rubikloud/gpdb,Postgres-XL/Postgres-XL,tangp3/gpdb,atris/gpdb,xuegang/gpdb,Chibin/gpdb,arcivanov/postgres-xl,lisakowen/gpdb,zaksoup/gpdb,atris/gpdb,lintzc/gpdb,rubikloud/gpdb,randomtask1155/gpdb,chrishajas/gpdb,oberstet/postgres-xl,ahachete/gpdb,adam8157/gpdb,cjcjameson/gpdb,greenplum-db/gpdb,edespino/gpdb,foyzur/gpdb,rubikloud/gpdb,tangp3/gpdb,ashwinstar/gpdb,50wu/gpdb,snaga/postgres-xl,tangp3/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,CraigHarris/gpdb,randomtask1155/gpdb,zaksoup/gpdb,lisakowen/gpdb,Postgres-XL/Postgres-XL,50wu/gpdb,xuegang/gpdb,Quikling/gpdb,chrishajas/gpdb,xuegang/gpdb,xuegang/gpdb,xinzweb/gpdb,Quikling/gpdb,Postgres-XL/Postgres-XL,tpostgres-projects/tPostgres,jmcatamney/gpdb,rvs/gpdb,xinzweb/gpdb,ovr/postgres-xl,cjcjameson/gpdb,tpostgres-projects/tPostgres,yuanzhao/gpdb,Quikling/gpdb,Chibin/gpdb,cjcjameson/gpdb,adam8157/gpdb,lpetrov-pivotal/gpdb,ahachete/gpdb,jmcatamney/gpdb,atris/gpdb,lpetrov-pivotal/gpdb,arcivanov/postgres-xl,lisakowen/gpdb,0x0FFF/gpdb,techdragon/Postgres-XL,zeroae/postgres-xl,janebeckman/gpdb,Quikling/gpdb,zeroae/postgres-xl,kaknikhil/gpdb,janebeckman/gpdb,ashwinstar/gpdb,royc1/gpdb,tangp3/gpdb,postmind-net/postgres-xl,50wu/gpdb,50wu/gpdb,kaknikhil/gpdb,zaksoup/gpdb,kaknikhil/gpdb,Quikling/gpdb,techdragon/Postgres-XL,kmjungersen/PostgresXL,lisakowen/gpdb,randomtask1155/gpdb,Quikling/gpdb,0x0FFF/gpdb,adam8157/gpdb,foyzur/gpdb,xuegang/gpdb,rubikloud/gpdb,adam8157/gpdb,lintzc/gpdb,Chibin/gpdb,chrishajas/gpdb,kaknikhil/gpdb,ashwinstar/gpdb,zeroae/postgres-xl,ahachete/gpdb,xuegang/gpdb,0x0FFF/gpdb,chrishajas/gpdb,lisakowen/gpdb,ovr/postgres-xl,rvs/gpdb,chrishajas/gpdb,xinzweb/gpdb,edespino/gpdb,Chibin/gpdb,royc1/gpdb,xuegang/gpdb,janebeckman/gpdb