gh-95251: IDLE - Add What's New section to README (GH-95688) (GH-95726)

Document what I (TJR) currently do for 3.10/3.11.

Co-authored-by: Erlend E. Aasland <erlend.aasland@protonmail.com>
(cherry picked from commit a302a274892f2dad4e1fa492c4886d55e4df0a80)

Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>