Add site/index.html

[sol]

This is mostly functional, but:

• The link to the privacy policy is broken (possible to fix, I guess)
• Assets are loaded from webflow.com (with a redirect via archive.org)
• Contains tracking JS (GA, ...)
• Uses Google web fonts
• Isn't tidy

I'm not going to work on this, but anybody is welcome to take over.

[moodmosaic]

Thank you, @sol 👍 If we serve this from haskell-hedgehog, which I think is possible, perhaps we won't need a new repo just for the GitHub Pages (e.g. we might not need hedgehogqa/hedgehogqa.github.io).