Add note distinguishing concurrent.futures.Future from asyncio.Future

Author: aisk

Doc/library/asyncio-future.rst

@@ -254,6 +254,8 @@ the Future has a result::
     asyncio.run(main())
 
 
+.. _asyncio-vs-concurrent-futures:
+
 .. important::
 
    The Future object was designed to mimic

Doc/library/concurrent.futures.rst

@@ -21,6 +21,13 @@ or separate processes, using :class:`ProcessPoolExecutor`.
 Each implements the same interface, which is defined
 by the abstract :class:`Executor` class.
 
+.. important::
+
+   :class:`concurrent.futures.Future` must not be confused with
+   :class:`asyncio.Future`, which is designed for use with :mod:`asyncio`
+   tasks and coroutines. See :ref:`asyncio-vs-concurrent-futures` for a
+   detailed comparison of the two.
+
 .. include:: ../includes/wasm-notavail.rst
 
 Executor Objects