bpo-41543: contextlib.nullcontext can fill in for an async context manager (GH-21870)

Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>
diff --git a/Doc/library/contextlib.rst b/Doc/library/contextlib.rst
index d5a1068..91edbba 100644
--- a/Doc/library/contextlib.rst
+++ b/Doc/library/contextlib.rst
@@ -243,8 +243,26 @@
           with cm as file:
               # Perform processing on the file
 
+   It can also be used as a stand-in for
+   :ref:`asynchronous context managers <async-context-managers>`::
+
+       async def send_http(session=None):
+          if not session:
+              # If no http session, create it with aiohttp
+              cm = aiohttp.ClientSession()
+          else:
+              # Caller is responsible for closing the session
+              cm = nullcontext(session)
+
+          async with cm as session:
+              # Send http requests with session
+
    .. versionadded:: 3.7
 
+   .. versionchanged:: 3.10
+      :term:`asynchronous context manager` support was added.
+
+
 
 .. function:: suppress(*exceptions)