Add additional example of REST API access with password on Yun

It is not clear how to access the API with password. Maybe a few examples will help. See http://forum.arduino.cc/index.php?topic=232957.msg1679448#msg1679448

Start with the linked Arduino forum discussion to understand the password-based Yun REST API access and identify the appropriate documentation or example location. Add a few clear examples showing access with a password; done means the Yun API documentation explains this workflow without requiring the forum thread.

Written by the indexing model from the issue text.