Call out 'get_value' and 'get_attribute'

docs/topics/3.0-announcement.md

@@ -562,7 +562,26 @@ The `MultipleChoiceField` class has been added. This field acts like `ChoiceFiel
 
 The `from_native(self, value)` and `to_native(self, data)` method names have been replaced with the more obviously named `to_internal_value(self, data)` and `to_representation(self, value)`.
 
-The `field_from_native()` and `field_to_native()` methods are removed.
+The `field_from_native()` and `field_to_native()` methods are removed. Previously you could use these methods if you wanted to customise the behaviour in a way that did not simply lookup the field value from the object. For example...
+
+    def field_to_native(self, obj, field_name):
+        """A custom read-only field that returns the class name."""
+        return obj.__class__.__name__
+
+Now if you need to access the entire object you'll instead need to override one or both of the following:
+
+* Use `get_attribute` to modify the attribute value passed to `to_representation()`.
+* Use `get_value` to modify the data value passed `to_internal_value()`.
+
+For example:
+
+    def get_attribute(self, obj):
+        # Pass the entire object through to `to_representation()`,
+        # instead of the standard attribute lookup.
+        return obj
+
+    def to_representation(self, value):
+        return value.__class__.__name__
 
 #### Explicit `queryset` required on relational fields.