Add pointer to IDLE what's new file.

Doc/whatsnew/3.4.rst

@@ -967,6 +967,16 @@ a ``-b/--bind`` option that causes the server to listen on a specific address.
 (Contributed by Malte Swart in :issue:`17764`.)
 
 
+idlelib and IDLE
+----------------
+
+Since idlelib implements the IDLE shell and editor and is not intended for
+import by other programs, it gets improvements with every release. See
+:file:`Lib/idlelib/NEWS.txt` for a cumulative list of changes since 3.3.0,
+as well as changes made in future 3.4.x releases. This file is also available
+from the IDLE Help -> About Idle dialog. 
+
+
 importlib
 ---------