gh-87691: add an absolute path pathlib example in / operator docs (GH-100737)

The behaviour is fully explained a couple paragraphs above, but it may be useful to have a brief example to cover the behaviour.
(cherry picked from commit 1ae619c911ec8e096f83eeb7cc57fcd966950a3d)

Co-authored-by: Shantanu <12621235+hauntsaninja@users.noreply.github.com>
Automerge-Triggered-By: GH:hauntsaninja