bpo-41192: Add documentation of undocumented audit events (GH-21308)

diff --git a/Doc/c-api/file.rst b/Doc/c-api/file.rst
index ea027ee..ed3735a 100644
--- a/Doc/c-api/file.rst
+++ b/Doc/c-api/file.rst
@@ -82,6 +82,8 @@
 
    This function is safe to call before :c:func:`Py_Initialize`.
 
+   .. audit-event:: setopencodehook "" c.PyFile_SetOpenCodeHook
+
    .. versionadded:: 3.8