Issue #23530: Improve os.cpu_count() description.
Patch by Julian Taylor.
diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index 8703f8f..e74430d 100644
--- a/Doc/library/multiprocessing.rst
+++ b/Doc/library/multiprocessing.rst
@@ -869,8 +869,13 @@
 
 .. function:: cpu_count()
 
-   Return the number of CPUs in the system.  May raise
-   :exc:`NotImplementedError`.
+   Return the number of CPUs in the system.
+
+   This number is not equivalent to the number of CPUs the current process can
+   use.  The number of usable CPUs can be obtained with
+   ``len(os.sched_getaffinity(0))``
+
+   May raise :exc:`NotImplementedError`.
 
    .. seealso::
       :func:`os.cpu_count`