title: Django-ORM: Count number of groups of each user
body: <p>I know that I can get the number of groups each user has with this query:</p>
  
  <pre><code>User.objects.filter(groups__in=Group.objects.all()).annotate(Count('pk'))
  </code></pre>
  
  <p>But something is missing:</p>
  
  <p>The users which are in no group at all.</p>
  
  <p>How can I use the django orm to get all users annotated by their group count, incluse users with no group?</p>