[2.7] bpo-33856: Add "help" to the welcome message of IDLE (GH-7755) (GH-7758)

Make it the same as when one runs 'python'..
(cherry picked from commit 9d49f85064c388e2dddb9f8cb4ae1f486bc8d357)

Co-authored-by: Stéphane Wirtel <stephane@wirtel.be>
diff --git a/Lib/idlelib/PyShell.py b/Lib/idlelib/PyShell.py
index fdd7cb1..337530a 100755
--- a/Lib/idlelib/PyShell.py
+++ b/Lib/idlelib/PyShell.py
@@ -1040,7 +1040,7 @@
         return self.shell_title
 
     COPYRIGHT = \
-          'Type "copyright", "credits" or "license()" for more information.'
+          'Type "help", "copyright", "credits" or "license()" for more information.'
 
     def begin(self):
         self.resetoutput()