gh-72239: Add note distinguishing concurrent.futures.Future from asyncio.Future (GH-143288)

(cherry picked from commit a9ca49d)

Co-authored-by: AN Long <aisk@users.noreply.github.com>

Author: aisk

Doc/library/concurrent.futures.rst

@@ -21,6 +21,11 @@ or separate processes, using :class:`ProcessPoolExecutor`.
 Each implements the same interface, which is defined
 by the abstract :class:`Executor` class.
 
+:class:`concurrent.futures.Future` must not be confused with
+:class:`asyncio.Future`, which is designed for use with :mod:`asyncio`
+tasks and coroutines. See the :doc:`asyncio's Future <asyncio-future>`
+documentation for a detailed comparison of the two.
+
 .. include:: ../includes/wasm-notavail.rst
 
 Executor Objects