How to edit index.php on Invision Power Board

I would like to add ZopIM to my forums, but I don't know PHP so need advice on how to implement it to the website.

<!-- Start of Zopim Live Chat Script -->
<script type="text/javascript">
document.write(unescape("%3Cscript src='" + document.location.protocol + "//zopim.com/?H7K0yeudH430QYymV0y8bt3AIjwQBk2v' charset='utf-8' type='text/javascript'%3E%3C/script%3E"));
</script>
<!-- End of Zopim Live Chat Script -->

Code (markup):

So how will it need to be added in the index.php file? (Where I assume it needs to go)

Index.php:

<?php
/**
 * <pre>
 * Invision Power Services
 * IP.Board v3.1.2
 * Main public executable wrapper.
 * Set-up and load module to run
 * Last Updated: $Date: 2010-01-15 10:18:44 -0500 (Fri, 15 Jan 2010) $
 * </pre>
 *
 * @author 		$Author: bfarber $
 * @copyright	(c) 2001 - 2009 Invision Power Services, Inc.
 * @license		http://www.invisionpower.com/community/board/license.html
 * @package		IP.Board
 * @link		http://www.invisionpower.com
 * @version		$Rev: 5713 $
 *
 */


define( 'IPB_THIS_SCRIPT', 'public' );
require_once( './initdata.php' );

require_once( IPS_ROOT_PATH . 'sources/base/ipsRegistry.php' );
require_once( IPS_ROOT_PATH . 'sources/base/ipsController.php' );

ipsController::run();

exit();

Code (markup):

 

It should be easy.. help, please.