docs: Added YouTube link to Android Auto Voice Actions video.

<a href="{@docRoot}training/managing-audio/index.html">Managing Audio Playback</a>, and

<a href="{@docRoot}guide/topics/media/exoplayer.html">ExoPlayer</a>.</p>

<a class="notice-developers-video wide"

href="https://www.youtube.com/watch?v=xc2HZSwPcwM">

<div>

    <h3>Video</h3>

    <p>Devbytes: Android Auto Voice Actions</p>

</div>

</a>

<h2 id="support_voice">Support Voice Actions</h2>

<p>To reduce driver distractions, you can add voice actions in your audio playback app. With voice