[3.12] gh-86206: Change IDLE splash line (GH-129698) (#129718)

Replace references to boilerplate files available in About IDLE and instead suggest clicking Help menu.

(cherry picked from commit d83a8a26f5e321b26bec59f5fd47c9c46c16ab12)

Co-authored-by: Stan Ulbrych <89152624+StanFromIreland@users.noreply.github.com>
Co-authored-by: Terry Jan Reedy <tjreedy@udel.edu>