title: Registering Django system checks in AppConfig's ready() method
body: <p>In the docs for Django's <a href="https://docs.djangoproject.com/en/1.8/topics/checks/#registering-and-labeling-checks">System check framework</a> it says:</p>
  
  <blockquote>
    <p>Checks should be registered in a file that’s loaded when your application is loaded; for example, in the <a href="https://docs.djangoproject.com/en/1.8/ref/applications/#django.apps.AppConfig.ready"><code>AppConfig.ready()</code></a> method.</p>
  </blockquote>
  
  <p>None of the examples on that page, or around the <code>AppConfig.ready()</code> method, show how to do this. Given a checking method like:</p>
  
  <pre><code>from django.core.checks import register, Tags
  
  @register(Tags.compatibility)
  def my_check(app_configs, **kwargs):
      # ... perform compatibility checks and collect errors
      return errors
  </code></pre>
  
  <p>How would you do this in/from the <code>AppConfig.ready()</code> method? Is one called from the other? Which file should the above method go in? Do you add <code>@register(...)</code> to the <code>ready()</code> method?</p>