[3.13] Docs: multi-disk ZIP files -> multipart ZIP files (GH-141962) (#142075)

Docs: multi-disk ZIP files -> multipart ZIP files (GH-141962)

* Remove some old currentlies
* multi-disk -> multipart
* Sentence case headings
(cherry picked from commit 890fe5aad55d4f28cda56834f9457ff79e9e8c60)

Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>