docs: Add link to "Voice search in your app" video.

    <li>"search for cat videos on myvideoapp"</li>

  </ul>

</div>

<!-- Video box -->

<a class="notice-developers-video"

   href="https://www.youtube.com/watch?v=PS1FbB5qWEI">

<div>

    <h3>Video</h3>

    <p>Voice search in your app</p>

</div>

</a>

<p>To support search within the context of your app, declare an intent filter in your app with

the <code>SEARCH_ACTION</code> action, as shown in the example intent filter below.</p>