gh-115634: document ProcessPoolExecutor max_tasks_per_child bug

Author: gpshead

Doc/library/concurrent.futures.rst

@@ -379,6 +379,11 @@ in a REPL or a lambda should not be expected to work.
    default in absence of a *mp_context* parameter. This feature is incompatible
    with the "fork" start method.
 
+   .. note::
+      Bugs have been reported when using the *max_tasks_per_child* feature that
+      can result in the :class:`ProcessPoolExecutor` hanging in some
+      circumstances. Follow its eventual resolution in :gh:`115634`.
+
    .. versionchanged:: 3.3
       When one of the worker processes terminates abruptly, a
       :exc:`~concurrent.futures.process.BrokenProcessPool` error is now raised.