Add PEP 573 additions to What's New (GH-21374)

Author: encukou

Doc/whatsnew/3.9.rst

@@ -1024,6 +1024,13 @@ C API Changes
 New Features
 ------------
 
+* :pep:`573`: Add :c:func:`PyType_FromModuleAndSpec` to associate
+  a module with a class; :c:func:`PyType_GetModule` and
+  :c:func:`PyType_GetModuleState` to retrieve the module and its state; and
+  :c:data:`PyCMethod` and :c:data:`METH_METHOD` to allow a method to
+  access the class it was defined in.
+  (Contributed by Marcel Plch and Petr Viktorin in :issue:`38787`.)
+
 * Add :c:func:`PyFrame_GetCode` function: get a frame code.
   Add :c:func:`PyFrame_GetBack` function: get the frame next outer frame.
   (Contributed by Victor Stinner in :issue:`40421`.)