Add link to changes-beta-1.html in header file.

Author: rachelbaker

_includes/header.html

@@ -4,6 +4,7 @@
 		<h1><a href="{{ site.baseurl }}">WP REST API v2 Documentation</a></h1>
 		<ul>
 			<li><a href="{{ site.baseurl }}">Home</a></li>
+			<li><a href="{{ site.baseurl }}changes-beta-1.html">What Changed</a></li>
 			<li><a href="https://github.com/WP-API/WP-API">WP REST API v2 Source</a></li>
 <!--       <li><a href="{{ site.baseurl }}guides.html">Guides</a></li>
 			<li><a href="{{ site.baseurl }}internals.html">Internals</a></li>