Merge pull request #453 from yprez/docs_fix

api-guide/views.md - add imports to code example

docs/api-guide/views.md

@@ -19,6 +19,10 @@ Using the `APIView` class is pretty much the same as using a regular `View` clas
 
 For example:
 
+    from rest_framework.views import APIView
+    from rest_framework.response import Response
+    from rest_framework import authentication, permissions
+
     class ListUsers(APIView):
         """
         View to list all users in the system.