Clarify in which Emacs version cl-lib is built-in

Author: purcell

README.md

@@ -72,8 +72,8 @@ install the package `.tar`-file via `M-x package-install-file`
 
 Note that in this case you will also need to have a sufficiently
 recent version of `cl-lib.el`, upon which `haskell-mode` depends.
-This is bundled with Emacs 24.x, and a backported version for use with
-Emacs 23 can be obtained from
+This is bundled with Emacs 24.3 and later, and a backported version
+for use with older Emacs versions can be obtained from
 [GNU ELPA](http://elpa.gnu.org/packages/cl-lib.html).
 
 #### MELPA