bpo-36669: add matmul support to weakref.proxy (GH-12932)

diff --git a/Doc/library/weakref.rst b/Doc/library/weakref.rst
index 7f3d267..80a908b 100644
--- a/Doc/library/weakref.rst
+++ b/Doc/library/weakref.rst
@@ -139,6 +139,10 @@
    prevent their use as dictionary keys.  *callback* is the same as the parameter
    of the same name to the :func:`ref` function.
 
+   .. versionchanged:: 3.8
+      Extended the operator support on proxy objects to include the matrix
+      multiplication operators ``@`` and ``@=``.
+
 
 .. function:: getweakrefcount(object)