bpo-21314: Add a FAQ entry about positional only parameters (GH-10641)

(cherry picked from commit 1aeeaeb79efa4de41f97b58547e23c2965ecabc5)

Co-authored-by: Lysandros Nikolaou <lisandrosnik@gmail.com>
diff --git a/Doc/library/functions.rst b/Doc/library/functions.rst
index b28f28f..9326b8d 100644
--- a/Doc/library/functions.rst
+++ b/Doc/library/functions.rst
@@ -668,6 +668,11 @@
    topic, and a help page is printed on the console.  If the argument is any other
    kind of object, a help page on the object is generated.
 
+   Note that if a slash(/) appears in the parameter list of a function, when
+   invoking :func:`help`, it means that the parameters prior to the slash are
+   positional-only. For more info, see
+   :ref:`the FAQ entry on positional-only parameters <faq-positional-only-arguments>`.
+
    This function is added to the built-in namespace by the :mod:`site` module.
 
    .. versionchanged:: 3.4