Automated deployment of web documentation

[palmskog]

By activating GitHub Pages, this repo can now deploy documentation for every new commit that would live at https://coq-community.org/coq-tricks

There are two kinds of documentation that I think can be appropriate:

• deployment of README.md as the index page HTML, see for example http://coq-community.org/awesome-coq
• deployment of documentation of the Coq code generated by a tool, see for example https://coq-community.org/aac-tactics/docs/coqdoc/toc.html

While using Alectryon would be nice, it currently relies on the SerAPI library that will not be maintained after Coq 8.20. I don't know if/when Alectryon will be ported to some other solution like Coq-LSP.