Add version added info for with statement and context managers
diff --git a/Doc/ref/ref3.tex b/Doc/ref/ref3.tex
index dfd4102..48a37f1 100644
--- a/Doc/ref/ref3.tex
+++ b/Doc/ref/ref3.tex
@@ -2109,6 +2109,8 @@
\subsection{Context Managers and Contexts\label{context-managers}}
+\versionadded{2.5}
+
A \dfn{context manager} is an object that manages the entry to, and exit
from, a \dfn{context} surrounding a block of code. Context managers are
normally invoked using the \keyword{with} statement (described in