📝 Mention avoiding PR numbers @ change notes

CHANGES/README.rst

@@ -36,6 +36,9 @@ telling the readers **what changed** in a specific version of
 the library *since the previous version*. You should also use
 *reStructuredText* syntax for highlighting code (inline or block),
 linking parts of the docs or external sites.
+However, you do not need to reference the issue or PR numbers here
+as *towncrier* will automatically add a reference to all of the
+affected issues when rendering the news file.
 If you wish to sign your change, feel free to add ``-- by
 :user:`github-username``` at the end (replace ``github-username``
 with your own!).