address review: add old discussion link

Author: skirpichev

peps/pep-0791.rst

@@ -7,7 +7,8 @@ Status: Draft
 Type: Standards Track
 Created: 12-May-2025
 Python-Version: 3.15
-Post-History: 02-Jun-2019,
+Post-History: `12-Jul-2018 <https://mail.python.org/archives/list/python-ideas@python.org/thread/YYJ5YJBJNCVXQWK5K3WSVNMPUSV56LOR/>`__,
+              02-Jun-2019,
               `09-May-2025 <https://discuss.python.org/t/91337>`__,