Just a few things markdownlint caught in https://github.com/twbs/bootstrap/tree/main-xmr-markdownlint
Unfortunately, we can't add markdownlint due to the FPs we are getting due to Hugo.
Also, the rules I went with are lax, I went mostly for consistency, but we could adapt the other branch and then the fixes here.
UNTESTED
Preview: https://deploy-preview-37255--twbs-bootstrap.netlify.app/