title: How to append extra data to the existing serializer in django
body: <p>I am new to django rest-framework serializers.</p>
  
  <pre><code>views.py 
  @csrf_exempt
  @api_view(['GET'])         
  def getAllAvailableEmps(request):  
      if request.method == 'GET':
          try:
              roleId = request.GET['emp_role_id']
              getEmp = emp_details.objects.filter(emp_dc_id = None,emp_active = True,emp_role_id = roleId)
              serializer = getEmpDcSerializer(getEmp,many=True)
              return JSONResponse({"allAvilableEmps":serializer.data})
          except Exception as e:
              return JSONResponse("Failure "+str(e)) 
  
  serializers.py
  class getEmpDcSerializer(serializers.ModelSerializer): 
      class Meta:
          model = emp_details
          fields = ('emp_id','emp_dc_id','emp_first_name','emp_last_name','emp_role_id')
  </code></pre>
  
  <p>from the above code i got the result like below</p>
  
  <pre><code>{
    "allAvilableEmps": [
      {
        "emp_id": 13,
        "emp_dc_id": [],
        "emp_first_name": "aaa",
        "emp_last_name": "bb",
        "emp_role_id": 4
      },
      {
        "emp_id": 16,
        "emp_dc_id": [],
        "emp_first_name": "cccc",
        "emp_last_name": "ddd",
        "emp_role_id": 4
      }
  ]
  }
  </code></pre>
  
  <p>Here,I need to add two more fields(Available,Assign) to the JOSN data.Like below(which is not exist in the database)..
  So final JSON should be like below. How to achieve this ?.</p>
  
  <pre><code>{
    "allAvilableEmps": [
      {
        "emp_id": 13,
        "emp_dc_id": [],
        "emp_first_name": "aaa",
        "emp_last_name": "bb",
        "emp_role_id": 4
        "Available":1,
        "Assign":2    
      },
      {
        "emp_id": 16,
        "emp_dc_id": [],
        "emp_first_name": "cccc",
        "emp_last_name": "ddd",
        "emp_role_id": 4
        "Available":1,
        "Assign":2    
      }
    ]
  }
  </code></pre>