[3.13] gh-149902: Remove dead packaging docs link and add a new section for external resources (GH-150030) (#150239)

Co-authored-by: Mia Albert <micha@2231puppy.tech>
Co-authored-by: Stan Ulbrych <stan@python.org>
Co-authored-by: Ned Batchelder <ned@nedbatchelder.com>
Co-authored-by: Hugo van Kemenade <1324225+hugovk@users.noreply.github.com>