Use a versionchanged directive.
diff --git a/Doc/library/warnings.rst b/Doc/library/warnings.rst
index d031b15..076d357 100644
--- a/Doc/library/warnings.rst
+++ b/Doc/library/warnings.rst
@@ -196,8 +196,11 @@
*module_globals*, if supplied, should be the global namespace in use by the code
for which the warning is issued. (This argument is used to support displaying
- source for modules found in zipfiles or other non-filesystem import sources, and
- was added in Python 2.5.)
+ source for modules found in zipfiles or other non-filesystem import
+ sources).
+
+ .. versionchanged:: 2.5
+ Added the `module_globals` parameter.
.. function:: warnpy3k(message[, category[, stacklevel]])