Add README for lib/sql
Add README for lib/sql

nyimbi/cartodb,dbirchak/cartodb,future-analytics/cartodb,thorncp/cartodb,CartoDB/cartodb,nuxcode/cartodb,raquel-ucl/cartodb,thorncp/cartodb,nuxcode/cartodb,dbirchak/cartodb,DigitalCoder/cartodb,codeandtheory/cartodb,codeandtheory/cartodb,UCL-ShippingGroup/cartodb-1,splashblot/dronedb,splashblot/dronedb,bloomberg/cartodb,nuxcode/cartodb,bloomberg/cartodb,nyimbi/cartodb,CartoDB/cartodb,future-analytics/cartodb,raquel-ucl/cartodb,codeandtheory/cartodb,thorncp/cartodb,DigitalCoder/cartodb,CartoDB/cartodb,raquel-ucl/cartodb,UCL-ShippingGroup/cartodb-1,CartoDB/cartodb,thorncp/cartodb,bloomberg/cartodb,CartoDB/cartodb,nuxcode/cartodb,raquel-ucl/cartodb,bloomberg/cartodb,bloomberg/cartodb,dbirchak/cartodb,codeandtheory/cartodb,future-analytics/cartodb,future-analytics/cartodb,future-analytics/cartodb,DigitalCoder/cartodb,nuxcode/cartodb,codeandtheory/cartodb,dbirchak/cartodb,nyimbi/cartodb,UCL-ShippingGroup/cartodb-1,UCL-ShippingGroup/cartodb-1,UCL-ShippingGroup/cartodb-1,nyimbi/cartodb,DigitalCoder/cartodb,DigitalCoder/cartodb,thorncp/cartodb,nyimbi/cartodb,splashblot/dronedb,raquel-ucl/cartodb,splashblot/dronedb,dbirchak/cartodb,splashblot/dronedb