Add Github pages for reading the spec

[christianparpart]

the github page should:

• allow reading the spec online right from that page (maybe the markdown version and optionally a link to the PDF)?
• have a link to the actual github repo
• this should somehow be auto-generated via CI (Github Actions), just like currently done with the (pre-)releases

[wez]

I don't have bandwidth for this directly, but you could potentially leverage https://github.com/wez/wezterm/blob/main/.github/workflows/pages.yml which is the action I use to publish the wezterm docs to gh_pages using mdbook. I don't think you need mdbook for this; the key thing is the publish stage at the bottom: https://github.com/wez/wezterm/blob/main/.github/workflows/pages.yml#L44

[christianparpart]

Thanks for that! :)