title: Showing more than '__str__' for a Django foreign key field
body: <p>I've two simple Django model classes,</p>
  
  <h1>models.py</h1>
  
  <pre><code>from django.db import models
  
  class ParentModel(models.Model):
      small_text = models.CharField(max_length=20)
      big_text = models.CharField(max_length=500)
  
      def __str__(self):
          return self.small_text
  
  
  class ChildModel(models.Model):
      parent = models.ForeignKey(ParentModel)
  
      def __str__(self):
          return '%s is my parent' % self.parent
  </code></pre>
  
  <h1>admin.py</h1>
  
  <pre><code>from django.contrib import admin
  import models
  
  admin.site.register(models.ChildModel)
  admin.site.register(models.ParentModel)
  </code></pre>
  
  <p>So the default view is you see the 'small_text' in a select element in the admin section.  What I'd love to be able to do is extend that so that there's another TextArea, or something else I can , underneath the select which changes as you choose a different Daddy.</p>
  
  <p>I've looked into a few different ways to do this, but they all seem hella complicated for what with Django, I'd have thought should be an easy task.  Any ideas?</p>