docs: Fixed broken link to M testing guide.

method. Even if your app is not targeting Android 6.0 (API level 23), you should test your app under

the new permissions model.</p>

<p>For details on supporting the new permissions model in your app, see the

<p>For details on supporting the new permissions model in your app, see

<a href="{@docRoot}training/permissions/index.html">

Permissions</a> training page. For tips on how to assess the impact on your app,

see the <a href="{@docRoot}about/versions/marshmallow/testing.html">Testing Guide</a></p>

Working with System Permissionss</a>. For tips on how to assess the impact on your app,

see <a href="{@docRoot}training/permissions/best-practices.html#testing">Permissions Best Practices</a>.</p>

<h2 id="behavior-power">Doze and App Standby</h2>

<p>This release introduces new power-saving optimizations for idle devices and apps. These