bpo-36888: Add multiprocessing.parent_process() (GH-13247)

diff --git a/Doc/library/multiprocessing.rst b/Doc/library/multiprocessing.rst
index c6ffb00..cc6dd4e 100644
--- a/Doc/library/multiprocessing.rst
+++ b/Doc/library/multiprocessing.rst
@@ -944,6 +944,14 @@
 
    An analogue of :func:`threading.current_thread`.
 
+.. function:: parent_process()
+
+   Return the :class:`Process` object corresponding to the parent process of
+   the :func:`current_process`. For the main process, ``parent_process`` will
+   be ``None``.
+
+   .. versionadded:: 3.8
+
 .. function:: freeze_support()
 
    Add support for when a program which uses :mod:`multiprocessing` has been