Update docs to fix linting issues

[dklimpel]

Checklist

• [x] make test-all (UNIX) passes. CI will also test this
• [x] unit and/or integration tests are included (if applicable)
• [x] documentation is changed or added (if applicable)

Description of change

• Linting markdown in docs
• Bump linting gh action (fix warning for deprecated NodeJS)
• add mssing markdown files to linter CI

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📚 Documentation preview 📚: https://goss--904.org.readthedocs.build/en/904/

[aelsabbahy]

Enabled the job. Also, I set up a read the docs account here:

https://goss.readthedocs.io/en/latest/ (currently 404)

The link in your PR description gives me a 404.

I think this is really close, thank you for iterating on this, greatly appreciated!