title: Django AutoOneToOneField migration and existing entries
body: <p>Before starting working on new features, I had this model :</p>
  
  <pre><code>class AppUser(models.Model):
      user = models.OneToOneField(User, primary_key=True) #Django standard user
      # And various standard data that we don't need here
  </code></pre>
  
  <p>Now I needed to extend my database to store more information about the users I have in Django and I came accros <a href="https://github.com/skorokithakis/django-annoying" rel="nofollow noreferrer">django-annoying</a> to build relations between like this :</p>
  
  <pre><code>class TutorialProgression(models.Model):
      has_seen_home_tutorial = models.BooleanField(default=False)
      has_seen_revision_tutorial = models.BooleanField(default=False)
      has_seen_lists_tutorial = models.BooleanField(default=False)
  
  class AppUser(models.Model):
      user= models.OneToOneField(User, primary_key=True) #Django standard user
      # Various standard data
      tutorial_progression = AutoOneToOneField(TutorialProgression)
  </code></pre>
  
  <p>What it does here is that when a new <code>AppUser</code> is created, a brand new TutorialProgression would be as well. But I have a problem with existing entries. I tried to migrate my postgres database with theses modifications and it asks me to provide a one-off default or to add a default in my models.</p>
  
  <p>I understand this, but how should I proceed to give each existing <code>AppUser</code> a unique <code>TutorialProgression</code>?</p>