gh-129699: Add description to IDLE doc title (#129727)

Also extend the 'idlelib' section header. These additions affect both the displayed idle.html file and the contents.html file displayed by clicking the Complete table of contents link on the main docs.python.org page. (The module index entries are generated from the module name and synopsis within module files.)
---------

Co-authored-by: Terry Jan Reedy <[email protected]>

Author: StanFromIreland

Doc/library/idle.rst

@@ -1,7 +1,7 @@
 .. _idle:
 
-IDLE
-====
+IDLE --- Python editor and shell
+================================
 
 .. moduleauthor:: Guido van Rossum <[email protected]>
 
@@ -971,8 +971,8 @@ information.  The only current default extension is zzdummy, an example
 also used for testing.
 
 
-idlelib
--------
+idlelib --- implementation of IDLE application
+----------------------------------------------
 
 .. module:: idlelib
    :synopsis: Implementation package for the IDLE shell/editor.