Add IPv6 Listen

Trojan-gRPC-Caddy2／Nginx/README.md

@@ -6,6 +6,7 @@ Xray client <--- gRPC(TLS) ---> Caddy2 <--- gRPC(cleartext) ---> Xray server
 ```conf
 server {
 	listen 443 ssl http2 so_keepalive=on;
+        listen [::]:443 ssl http2 so_keepalive=on;
 	server_name example.com;
 
 	index index.html;