Update README.md

Author: xtutran

misc/README.md

@@ -13,6 +13,7 @@ pip install --proxy=http://[user:password@]<proxy server>:8080 xgboost
 ```
 
 ## Forward a port from remote server to localhost
+[Reference](https://www.ssh.com/ssh/tunneling/example)
 ```bash
 ssh -L <local port>:localhost:<remote port> <remote server>
 ```