gh-142044: Add note to prefer asyncio.timeout[_at] over asyncio.Timeout (GH-144449)

(cherry picked from commit 0e7c06a)

Co-authored-by: kovan <xaum.io@gmail.com>

Author: kovan

Doc/library/asyncio-task.rst

@@ -758,6 +758,9 @@ Timeouts
        An :ref:`asynchronous context manager <async-context-managers>`
        for cancelling overdue coroutines.
 
+       Prefer using :func:`asyncio.timeout` or :func:`asyncio.timeout_at`
+       rather than instantiating :class:`!Timeout` directly.
+
        ``when`` should be an absolute time at which the context should time out,
        as measured by the event loop's clock: