title: Need help understanding many and source fields in a serializer
body: <p>I am currently trying to familiarize myself with DRF and while going through a tutorial these serializers were used</p>
  <pre><code>class EmbeddedAnswerSerializer(serializers.ModelSerializer):
      votes = serializers.IntegerField(read_only=True)
  
      class Meta:
          model = Answer
          fields = ('id', 'text', 'votes',)
  
  
  class QuestionSerializer(serializers.ModelSerializer):
      answers = EmbeddedAnswerSerializer(many=True,source='answer_set')
      class Meta:
          model = Question
          fields = ('id', 'answers', 'created_at', 'text', 'user_id',)
  </code></pre>
  <p>These are the models</p>
  <pre><code>class Question(models.Model):
      user_id = models.CharField(max_length=36)
      text = models.CharField(max_length=140)
      created_at = models.DateTimeField(auto_now_add=True)
  
  
  class Answer(models.Model):
      question = models.ForeignKey(Question,on_delete=models.PROTECT)
      text = models.CharField(max_length=25)
      votes = models.IntegerField(default=0)
  </code></pre>
  <p>My question is in the statement in the Question serializer</p>
  <pre><code>answers = EmbeddedAnswerSerializer(many=True,source='answer_set')
  </code></pre>
  <p>what is the purpose of <code>many = True</code> and <code>source='answer_set'</code> ?
  I read from the documentation the following regarding <code>many=True</code></p>
  <blockquote>
  <p>You can also still use the many=True argument to serializer classes.
  It's worth noting that many=True argument transparently creates a
  ListSerializer instance, allowing the validation logic for list and
  non-list data to be cleanly separated in the REST framework codebase.</p>
  </blockquote>
  <p>I am confused by what that means? If I remove <code>many=True</code> from the code I get the error</p>
  <pre><code>AttributeError at /api/quest/1/2/
  Got AttributeError when attempting to get a value for field `text` on serializer `EmbeddedAnswerSerializer`.
  The serializer field might be named incorrectly and not match any attribute or key on the `RelatedManager` instance.
  Original exception text was: 'RelatedManager' object has no attribute 'text'.
  </code></pre>
  <p>Can anyone explain what <code>many=True</code> does and what <code>source</code> field does?</p>