docs: update Changelog.

docs/changelog.rst

@@ -235,6 +235,11 @@ Core Library
   was leaked on every RPC, due to a list of strong references keeping alive any
   handler ever registered for disconnect notification.
 
+* `#418 <https://github.com/dw/mitogen/issues/418>`_: the
+  :func:`mitogen.parent.iter_read` helper would leak poller FDs, because
+  execution of its :keyword:`finally` block was delayed on Python 3. Now
+  callers explicitly close the generator when finished.
+
 * `16ca111e <https://github.com/dw/mitogen/commit/16ca111e>`_: handle OpenSSH
   7.5 permission denied prompts when ``~/.ssh/config`` rewrites are present.