usually the Cloudron team is quick to pick up these suggestions, when they come up on the forum. But if you want to change it yourself the source of the documentation is located at https://git.cloudron.io/cloudron/docs/. All you need to make a pull request is an account on the Cloudron Gitlab installation.
the page where you can browse and download Roundcube plugins has been changed.
Is there a way that me as a user updates the page at https://docs.cloudron.io/apps/roundcube/ to reflect these changes?
It's important to note that many of these plugins are hopelessly out of date and not functional anymore using the current Roundcube version (i.e. https://packagist.org/packages/roundcube/customizr or all the keyboard shortcut plugins: https://forum.cloudron.io/post/60771).
Furthermore, the most current versions of such plugins are often in their respective GitHub repository, not on packagist (i.e. this whole plugin business is huge mess...).
I think that's the link listed in https://docs.cloudron.io/apps/roundcube/#plugins , maybe there is another link I am missing.
But as @fbartels said, feel free to submit changes to https://git.cloudron.io/cloudron/docs . App docs are at https://git.cloudron.io/cloudron/docs/-/tree/master/knowledgebase/docs/apps