title: Additional field while serializing django rest framework
body: <p>I am a newbie to django rest framework and have created a sample <code>Employee</code> model.</p>
  
  <p>My <strong>models.py</strong>:</p>
  
  <pre><code>class Employees(models.Model):
      created = models.DateTimeField(auto_now_add=True)
      first_name = models.CharField(max_length=100)
      last_name = models.CharField(max_length=100)
  </code></pre>
  
  <p>My <strong>serializers.py</strong>:</p>
  
  <pre><code>class EmployeeSerializer(serializers.Serializer):
      class Meta:
          model = Employees
          fields = ('first_name','last_name')
  </code></pre>
  
  <p>This works fine but I want an additional field <code>full_name</code>, which will be <code>first_name + last_name</code>.</p>
  
  <p>How do I define this new field <code>full_name</code> in my <code>serializers.py</code>?</p>