Everyone can submit a plugin to the Resources page. It just need something called a KDE Identity, which is a login for a few other KDE platforms (like an old KDE forum).
- Register on identity.kde.org if you haven’t already.
- Go to invent.kde.org and login.
- Go to this page: resources_page.rst · master · Documentation / Krita.org Documentation Website · GitLab
- Click “Edit” on top, scroll down and add a little description and the link

Detailed instructions here: Krita Manual Contribution Guide — Krita Manual 5.0.0 documentation