bpo-33725, multiprocessing doc: rephase warning against fork on macOS (GH-13841)

Co-Authored-By: Barry Warsaw <barry@python.org>
diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index 6c07124..d8182fe 100644
--- a/Doc/library/multiprocessing.rst
+++ b/Doc/library/multiprocessing.rst
@@ -126,8 +126,9 @@
 
 .. versionchanged:: 3.8
 
-   On macOS, *spawn* start method is now the default: *fork* start method is no
-   longer reliable on macOS, see :issue:`33725`.
+   On macOS, the *spawn* start method is now the default.  The *fork* start
+   method should be considered unsafe as it can lead to crashes of the
+   subprocess. See :issue:`33725`.
 
 .. versionchanged:: 3.4
    *spawn* added on all unix platforms, and *forkserver* added for