title: Automatic 'created by user' field using django-rest-framework?
body: <h3>models.py</h3>
  
  <pre><code>class Nugget(TimeStampedModel):
      added_by = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.SET_NULL, related_name='added_by', blank=True, null=True)
  </code></pre>
  
  <h3>serializers.py</h3>
  
  <pre><code>class NuggetSerializer(TaggitSerializer, serializers.ModelSerializer):
      added_by = serializers.CreateOnlyDefault(default=serializers.CurrentUserDefault())
  </code></pre>
  
  <h3>views.py</h3>
  
  <pre><code>class NuggetList(generics.ListCreateAPIView):
      queryset = Nugget.objects.all()
      serializer_class = NuggetSerializer
  
      def perform_create(self, serializer):
          serializer.save(added_by=self.request.user)
  </code></pre>
  
  <h3>What I'm trying to achieve:</h3>
  
  <p><code>added_by</code> should:</p>
  
  <ol>
  <li>Be set on <code>create</code> of a <code>Nugget</code></li>
  <li>Default to the <code>user</code> who created the <code>Nugget</code>, with no way to override this default</li>
  <li>Be included and shown when a <code>Nugget</code> is retrieved</li>
  <li>Not be shown as an option for <code>create/POST</code> in the browsable API</li>
  <li>Not be editable after <code>create</code></li>
  </ol>