bpo-38892: Improve docs for audit event (GH-17361)

diff --git a/Doc/library/audit_events.rst b/Doc/library/audit_events.rst
index c23b9c6..3c68a15 100644
--- a/Doc/library/audit_events.rst
+++ b/Doc/library/audit_events.rst
@@ -7,7 +7,7 @@
 
 This table contains all events raised by :func:`sys.audit` or
 :c:func:`PySys_Audit` calls throughout the CPython runtime and the
-standard library.
+standard library.  These calls were added in 3.8.0 or later.
 
 See :func:`sys.addaudithook` and :c:func:`PySys_AddAuditHook` for
 information on handling these events.