Added hint for nginx path

Setup-Reverse-Proxy.md

@@ -17,7 +17,7 @@ http {
                 proxy_set_header        Host            $http_host;
                 proxy_set_header        X-Forwarded-For $proxy_add_x_forwarded_for;
                 proxy_set_header        X-Scheme        $scheme;
-                proxy_set_header        X-Script-Name   /calibre;
+                proxy_set_header        X-Script-Name   /calibre;  # IMPORTANT: path has NO trailing slash 
         }
     }
 }