gh-90815: Document bundled mimalloc in What’s New In Python 3.13 (GH-117811)

Author: hroncok

Doc/license.rst

@@ -1042,6 +1042,8 @@ https://www.w3.org/TR/xml-c14n2-testcases/ and is distributed under the
    OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 
+.. _mimalloc-license:
+
 mimalloc
 --------
 

Doc/whatsnew/3.13.rst

@@ -1621,6 +1621,11 @@ Build Changes
 * ``wasm32-emscripten`` is no longer a :pep:`11` supported platform.
   (Contributed by Brett Cannon in :gh:`115192`.)
 
+* Python now bundles the `mimalloc library <https://github.com/microsoft/mimalloc>`__.
+  It is licensed under the MIT license, see :ref:`mimalloc license <mimalloc-license>`.
+  The bundled mimalloc has custom changes, see :gh:`113141` for details.
+  (Contributed by Dino Viehland in :gh:`109914`.)
+
 
 C API Changes
 =============