Add PEP 747 to release summary

Author: hugovk

Doc/whatsnew/3.15.rst

@@ -77,6 +77,8 @@ Summary -- Release highlights
   <whatsnew315-unpacking-in-comprehensions>`
 * :pep:`686`: :ref:`Python now uses UTF-8 as the default encoding
   <whatsnew315-utf8-default>`
+* :pep:`747`: :ref:`Annotating type forms with TypeForm
+  <whatsnew315-typeform>`
 * :pep:`782`: :ref:`A new PyBytesWriter C API to create a Python bytes object
   <whatsnew315-pep782>`
 * :ref:`The JIT compiler has been significantly upgraded <whatsnew315-jit>`
@@ -1438,6 +1440,8 @@ threading
 typing
 ------
 
+.. _whatsnew315-typeform:
+
 * :pep:`747`: Add :data:`~typing.TypeForm`, a new special form for annotating
   values that are themselves type expressions.
   ``TypeForm[T]`` means "a type form object describing ``T`` (or a type