Add some nginx headers

Thanks @robsalasco! I added this headers because saw your fork and thought that it will be pretty good to have these headers by default.

data/nginx/app.conf

@@ -21,6 +21,9 @@ server {
     ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem;
 
     location / {
-        proxy_pass http://example.org;
+        proxy_pass  http://example.org;
+        proxy_set_header    Host                $http_host;
+        proxy_set_header    X-Real-IP           $remote_addr;
+        proxy_set_header    X-Forwarded-For     $proxy_add_x_forwarded_for;
     }
 }