Update docs/versionhistory.rst

Co-authored-by: Ganden Schaffner <github@xqzw.me>

docs/versionhistory.rst

@@ -5,9 +5,10 @@ This library adheres to `Semantic Versioning 2.0 <http://semver.org/>`_.
 
 **UNRELEASED**
 
-- Fixed race condition in ``get_async_backend``
-  (`#425 <https://github.com/agronholm/anyio/issues/425>`_; PR by David Jiricek and
-  Ganden Schaffner)
+- Fixed a race condition that caused crashes when multiple event loops of the same
+  backend were running in separate threads and simultaneously attempted to use AnyIO for
+  their first time (`#425 <https://github.com/agronholm/anyio/issues/425>`_; PR by David
+  Jiricek and Ganden Schaffner)
 - Added the ``BlockingPortalProvider`` class to aid with constructing synchronous
   counterparts to asynchronous interfaces that would otherwise require multiple blocking
   portals