doc: Briefly mention C API changes in whatsnew.

diff --git a/Doc/whatsnew/3.5.rst b/Doc/whatsnew/3.5.rst
index 9325b9089c9852fe13cbc2e30dd769a6a039be5b..8a1bd91e2c47f58494465520aecd6de4ff821f7b 100644 (file)
--- a/Doc/whatsnew/3.5.rst
+++ b/Doc/whatsnew/3.5.rst
@@ -879,3 +879,6 @@ Changes in the C API
   introspection, a deprecation warning now is raised for builtin type without
   the :attr:`__module__` attribute.  Would be an AttributeError in future.
   (:issue:`20204`)
+
+* As part of PEP 492 implementation, ``tp_reserved`` slot of
+  ``PyTypeObject`` was replaced with ``tp_as_async`` slot.