docs: improvements to building and docs

[hacdias]

• Move the website stuff to www, while keeping the "known" GitHub files in the root of the repo (security, code of conduct, etc).
• Make a new page as the index of the website and update the README to mostly link to the website.
• Change the build website action to only run on PRs where the website files have been changed.
• Only use a single Docker image for building and developing the website.
• Do not publish Docker images for website, since we're using Cloudflare Pages.
• Removes the watch.sh script since I could not find a use for it
• Small updates to website (naming, add changelog, index)
• Remove some unnecessary markdown extensions