Link to html-validate.org for explanations of issues

It would be nice to display links to html-validate.org for explanations of issues in the default formatters.

Use cases

It would make it easier for users to single-click on the issue to find an explanation and some indication of how to address it. Currently it would be possible to do this using a custom formatter, but it would be great to have out-of-the-box support.

See for example: https://github.com/nuxt-community/html-validator-module/issues/39 and https://github.com/nuxt-community/html-validator-module/issues/1