Note version added for conditional expressions

Doc/ref/ref5.tex

@@ -1039,7 +1039,7 @@ The operator \keyword{not} yields \code{True} if its argument is false,
 The expression \code{\var{x} if \var{C} else \var{y}} first evaluates
 \var{C} (\emph{not} \var{x}); if \var{C} is true, \var{x} is evaluated and
 its value is returned; otherwise, \var{y} is evaluated and its value is
-returned.
+returned.  \versionadded{2.5}
 
 The expression \code{\var{x} and \var{y}} first evaluates \var{x}; if
 \var{x} is false, its value is returned; otherwise, \var{y} is