adding-a-package-manager.md

Closes #13953

Co-authored-by: Rhys Arkins <rhys@arkins.net>
Co-authored-by: Michael Kriese <michael.kriese@visualon.de>
Co-authored-by: HonkingGoose <34918129+HonkingGoose@users.noreply.github.com>

BREAKING CHANGE: languages are now called categories instead