title: Add logic to PATCH on Django Rest Framework
body: <p>In my very simple learning application, I would like to trigger some logic the moment that a model changes to 'complete'. Specifically, I pass the following payload to my viewset:</p>
  
  <pre><code>{
     complete: true
  }
  </code></pre>
  
  <p>which is as follows:</p>
  
  <pre><code>class TestQuestionViewset(viewsets.ModelViewSet):
  
      queryset = TestQuestion.objects.all()
      serializer_class = TestQuestionSerializer
  </code></pre>
  
  <p>I would like to trigger some logic server side that is triggered as soon as the complete flag is updated.</p>
  
  <p>Could I override the update method? If so, how could I do this?</p>