Clarify firewall-rule doc
Clarify firewall-rule doc

caicloud/ingress,caiyixiang/ingress,aledbf/ingress-nginx,canhnt/ingress,literalice/ingress,nevetS/ingress,matthewg/ingress,nevetS/ingress,kubernetes/ingress-gce,aledbf/ingress-nginx,literalice/ingress,kubernetes/ingress-nginx,kubernetes/ingress-nginx,nicksardo/ingress,matthewg/ingress,danielqsj/ingress,kubernetes/ingress-nginx,kubernetes/ingress-nginx,porridge/ingress,nicksardo/ingress,caicloud/ingress,canhnt/ingress,porridge/ingress,nicksardo/ingress,arjanschaaf/ingress,chentao1596/ingress,kubernetes/ingress-gce,caicloud/ingress,jcmoraisjr/ingress,jcmoraisjr/ingress,nicksardo/ingress,danielqsj/ingress,canhnt/ingress,aledbf/ingress-nginx,coryfklein/ingress,arjanschaaf/ingress,jcmoraisjr/ingress,winfield-chen-hs/ingress,canhnt/ingress,coryfklein/ingress,kubernetes/ingress-nginx,aledbf/ingress-nginx,winfield-chen-hs/ingress,caiyixiang/ingress,chentao1596/ingress,caicloud/ingress