readme: added note about command line args
readme: added note about command line args

zultron/docker-provisioning,sameersbn/docker-squid,korczis/docker-squid-rubygems-proxy,Optibus/docker-squid,linearregression/docker-squid-s3,maqsoodumt/docker-squid,boliu83/docker-squid,korczis/docker-squid-rubygems-proxy,opendoor-labs/docker-squid-s3