Update readme to indicate multiple PG versions
Update readme to indicate multiple PG versions

appropriate/docker-postgis,nullcode/docker-postgis,LukeSwart/appropriate-postgis,elcodedocle/docker-postgis,imatia-smartgovernment/docker-postgis,gpavlidi/docker-postgis,ajaali/docker-postgis,moofish32/docker-postgis,purpleP/docker-postgis-1