bpo-26836: Document os.memfd_create() name parameter (GH-13838) (GH-13839)

https://bugs.python.org/issue26836
(cherry picked from commit ccf0efbb21f6bbf6efd5f8cb560fed11079ce1a2)

Co-authored-by: Victor Stinner <vstinner@redhat.com>
diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index 107764b..f0df35e 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -3011,6 +3011,13 @@
    (or a bitwise ORed combination of them).  By default, the new file
    descriptor is :ref:`non-inheritable <fd_inheritance>`.
 
+   The name supplied in *name* is used as a filename and will be displayed as
+   the target of the corresponding symbolic link in the directory
+   ``/proc/self/fd/``. The displayed name is always prefixed with ``memfd:``
+   and serves only for debugging purposes. Names do not affect the behavior of
+   the file descriptor, and as such multiple files can have the same name
+   without any side effects.
+
    .. availability:: Linux 3.17 or newer with glibc 2.27 or newer.
 
    .. versionadded:: 3.8