Add note about port needed in NGINX config

lib/support/nginx/registry-ssl

@@ -16,6 +16,8 @@ server {
 }
 
 server {
+  # If a different port is specified in https://gitlab.com/gitlab-org/gitlab-ce/blob/8-8-stable/config/gitlab.yml.example#L182,
+  # it should be declared here as well
   listen *:443 ssl http2;
   server_name  registry.gitlab.example.com;
   server_tokens off; ## Don't show the nginx version number, a security best practice