bpo-23859: Document that asyncio.wait() does not cancel its futures (#7217)

Unlike `asyncio.wait_for()`, `asyncio.wait()` does not cancel the passed
futures when a timeout accurs.

Doc/library/asyncio-task.rst

@@ -768,6 +768,9 @@ Task functions
    |                             | futures finish or are cancelled.       |
    +-----------------------------+----------------------------------------+
 
+   Unlike :func:`~asyncio.wait_for`, ``wait()`` will not cancel the futures
+   when a timeout accurs.
+
    This function is a :ref:`coroutine <coroutine>`.
 
    Usage::

Misc/NEWS.d/next/Documentation/2018-05-29-16-02-31.bpo-23859.E5gba1.rst

+Document that `asyncio.wait()` does not cancel its futures on timeout.