Document Bootstrap5 under Contributed themes

Problem/Motivation

I see that documentation for Bootstrap5 has been created at https://www.drupal.org/docs/contributed-themes/bootstrap5-theme which is great.

I tried to create a sub-page under it, but couldn't. I believe the problem is that https://www.drupal.org/docs/contributed-themes/bootstrap5-theme is a Page, but it should have been a Guide, to allow pages to be added under it.

So I went ahead and created a new Guide: https://www.drupal.org/docs/contributed-themes/bootstrap5
Under the "Guide" I could add a "Page": https://www.drupal.org/docs/contributed-themes/bootstrap5/add-a-font-in-...

Steps to reproduce

Proposed resolution

Remaining tasks

• Add link Documentation under "Resources" on the right hand side of project page, above "Read license" and "View project translations"
• Check if the Page https://www.drupal.org/docs/contributed-themes/bootstrap5-theme (should have been a Guide) has been deleted in #3314318: Add some more documentation pages to their guide’s menu?. I added the task in that issue and not here, since it is related to drupalorg

User interface changes

API changes

Data model changes