Serializer fields section for 3rd-party packages

* Add new section to serializer fields page where we can list and link 3rd-party packages that provide more field types
* Add an entry for drf-compound-fields

docs/api-guide/fields.md

@@ -347,6 +347,14 @@ As an example, let's create a field that can be used represent the class name of
             """
             return obj.__class__
 
+# More fields from 3rd-party packages
+
+## [drf-compound-fields](http://drf-compound-fields.readthedocs.org)
+
+Provides "compound" serializer fields, such as lists of simple values, which can be described by
+other fields rather than serializers with the `many=True` option. Also provided are fields for
+typed dictionaries and values that can be either a specific type or a list of items of that type.
+
 [cite]: https://docs.djangoproject.com/en/dev/ref/forms/api/#django.forms.Form.cleaned_data
 [FILE_UPLOAD_HANDLERS]: https://docs.djangoproject.com/en/dev/ref/settings/#std:setting-FILE_UPLOAD_HANDLERS
 [ecma262]: http://ecma-international.org/ecma-262/5.1/#sec-15.9.1.15