Allow sending of HTML via setHTML method

Adds a section to index.php that makes it easier to send HTML to Glass. Uses existing setHTML() method in client API.

![screenshot-20130627-mirror-quickstart-php-section-addition](https://f.cloud.github.com/assets/643503/716514/7f8ae9c0-df37-11e2-97cb-3b24f24d1fd5.jpg)