doc(use): add ipv6 to nginx config

I added IPv6 to my RPC node so I'm sharing.

docs/user/rpc.md

@@ -20,6 +20,7 @@ server {
   server_name gdev.YOUR_DOMAIN.fr;
 
   listen 443 ssl http2;
+  listen [::]:443 ssl http2;
   ssl_certificate /etc/nginx/ssl/YOUR_DOMAIN.cert;
   ssl_certificate_key /etc/nginx/ssl/YOUR_DOMAIN.key;