title: Create OneToOne instance on model creation
body: <p>I'm building my first django app. I have a user, and the user has a list of favourites. A user has exactly one list of favourites, and that list belongs exclusively to that user.</p>
  
  <pre><code>class User(models.Model):
      name = models.CharField(max_length=200)
  
  class FavouriteList(models.Model):
      user = models.OneToOneField(User)
      favourites = models.ManyToManyField(Favourite, blank=True)
  </code></pre>
  
  <p>When a new user is created, I want to ensure that the user has a <code>FavouriteList</code>. I've looked around in the Django documentation and haven't had much luck.</p>
  
  <p>Does anyone know how I can ensure that a model has a child object (e.g. <code>FavouriteList</code>) when it is created?</p>