[3.13] GH-139067: Add example for `argparse`'s `append` action (GH-131389) (#139069)

GH-139067: Add example for `argparse`'s `append` action (GH-131389)
(cherry picked from commit 101fd33065638c94f413447a7bcff09d54831a4a)

Co-authored-by: Moshe Kaplan <mosheekaplan@gmail.com>