add instructions for cloudflare

Proxy-examples.md

@@ -184,6 +184,9 @@ server {
 
     proxy_set_header Host $host;
     proxy_set_header X-Real-IP $remote_addr;
+    # If you use Cloudflare proxying, replace $remote_addr with $http_cf_connecting_ip
+    # See https://developers.cloudflare.com/support/troubleshooting/restoring-visitor-ips/restoring-original-visitor-ips/#nginx-1
+    # alternatively use ngx_http_realip_module
     proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
     proxy_set_header X-Forwarded-Proto $scheme;