Change README to tell that it support more databases
Change README to tell that it support more databases

PostgreSQL and SQLite3 are supported now
perobertson/shipit-engine,perobertson/shipit-engine,Shopify/shipit-engine,ershad/shipit-engine,Shopify/shipit-engine,Shopify/shipit-engine,Shopify/shipit-engine,perobertson/shipit-engine,ershad/shipit-engine,Shopify/shipit-engine,ershad/shipit-engine,ershad/shipit-engine,perobertson/shipit-engine,ershad/shipit-engine,perobertson/shipit-engine