Merge "docs: Clarified structure of security config file." into mnc-mr-docs

<pre>

<?xml version="1.0" encoding="utf-8"?>

...

<manifest ... >

  <application ... >

    <meta-data android:name="android.security.net.config"

               android:resource="@xml/network_security_config" />

    ...

  </application>

</manifest>

</pre>

<h2 id="CustomTrust">Customizing Trusted CAs</h2>