bpo-42783: Documentation for asyncio.sleep(0) (#24002)

Co-authored-by: Ken Jin <28750310+Fidget-Spinner@users.noreply.github.com>

Author: simonw

Doc/library/asyncio-task.rst

@@ -293,6 +293,10 @@ Sleeping
    ``sleep()`` always suspends the current task, allowing other tasks
    to run.
 
+   Setting the delay to 0 provides an optimized path to allow other
+   tasks to run. This can be used by long-running functions to avoid
+   blocking the event loop for the full duration of the function call.
+
    .. _asyncio_example_sleep:
 
    Example of coroutine displaying the current date every second