issue #400: update Changelog.

docs/changelog.rst

@@ -50,6 +50,9 @@ Fixes
   now print a useful hint when Python fails to start, as no useful error is
   normally logged to the console by these tools.
 
+* `#400 <https://github.com/dw/mitogen/issues/400>`_: work around a threading
+  bug in the AWX display callback when running with high verbosity setting.
+
 * `#409 <https://github.com/dw/mitogen/issues/409>`_: the setns method was
   silently broken due to missing tests. Basic coverage was added to prevent a
   recurrence.
@@ -100,6 +103,7 @@ Mitogen would not be possible without the support of users. A huge thanks for
 bug reports, features and fixes in this release contributed by
 `Brian Candler <https://github.com/candlerb>`_,
 `Guy Knights <https://github.com/knightsg>`_,
+`Jiří Vávra <https://github.com/Houbovo>`_,
 `Jonathan Rosser <https://github.com/jrosser>`_, and
 `Mehdi <https://github.com/mehdisat7>`_.