Clarify the purpose of the wcag-act-rules repo

[dan-tripp-siteimprove]

Today in the office hours, the https://github.com/w3c/wcag-act-rules repo came up. It's unclear to me what that repo is. I think that the content of that repo is only about the technical aspects of the ACT website - i.e. that repo doesn't contain the content of the ACT rules. [edit: I looked again and I see now that it does contain that content, but it seems to be a copy, made from this repo.] But, to my surprise, it does contain issues about the content of the rules. (Example issue 1, example issue 2.) Should those issues be on this (the https://github.com/act-rules/act-rules.github.io) repo instead? Or are those issues on the right repo and there is some AGWG workflow which tells them to create issues on that repo rather than this one? Either way, I'd like to clarify this in the README for that repo and/or this repo.

[dan-tripp-siteimprove]

FYI @carlosapaduarte