Add version added info for with statement and context managers
diff --git a/Doc/lib/libcontextlib.tex b/Doc/lib/libcontextlib.tex
index 842c954..46f9cdd 100644
--- a/Doc/lib/libcontextlib.tex
+++ b/Doc/lib/libcontextlib.tex
@@ -4,6 +4,8 @@
 \declaremodule{standard}{contextlib}
 \modulesynopsis{Utilities for \keyword{with}-statement contexts.}
 
+\versionadded{2.5}
+
 This module provides utilities for common tasks involving the
 \keyword{with} statement.