style: add note class

[ac-willeke]

Example on how to create styling classes. We could also create different textboxes: .note .warning etc..

[anders-kolstad]

The checks failed with this erros:

remote: Permission to NINAnor/NINA-ebook-template.git denied to github-actions[bot].
fatal: unable to access 'https://github.com/NINAnor/NINA-ebook-template/': The requested URL returned error: 403

The repo did not give GH actions write permission, which its needs to render the book and add html files.
I think this is set at the NINAnor level, but we can bypass it in the project YAML (_quarto.yml) with this:

permissions:
  contents: read
  pages: write          # <-- Add this line

I have also added a branch protection over the main branch. That could block this again. But I made @ac-willeke admin so you can remove the branch protection if needed.

Also, there was a warning about missing packages:

Warning message:
The downlit and xml2 packages are required for code linking 

R packages can be specified in the DESCRIPTION file.

[ac-willeke]

• missing R packages are added to DESCRIPTION file
• permissions for pages set to write in workflow file: quarto-render.yml

Note: workflow runs correctly on the forked repo, but fails while running from NINAnor. This is due to the fact that the NINAnor repo is protected. Forks cannot get write access to the GITHUB_TOKEN and therefore workflow fails on this error:

remote: Permission to NINAnor/NINA-ebook-template.git denied to github-actions[bot].
fatal: unable to access 'https://github.com/NINAnor/NINA-ebook-template/': The requested URL returned error: 403

Info from GitHub docs

Changing the permissions in a forked repository
You can use the permissions key to add and remove read permissions for forked repositories, but typically you can't grant write access. The exception to this behavior is where an admin user has selected the Send write tokens to workflows from pull requests option in the GitHub Actions settings. For more information, see "Managing GitHub Actions settings for a repository."