title: Return nested serializer in serializer method field
body: <p>I have a method field called <code>followers</code>. I get the list of followers in a <code>SerializerMethodField</code> :</p>
  
  <pre><code>followers = serializers.SerializerMethodField()
  </code></pre>
  
  <p>I want to format the result with a specific serializer called <code>BaseUserSmallSerializer</code>. How should I implement the method <code>get_followers</code> to achieve that ?</p>