Link official docs in the readme

[vadosnaprimer]

While some of the docs are kept on tasvideos https://tasvideos.org/EmulatorResources/LibTAS there's also http://clementgallet.github.io/libTAS/help/ and I don't know how up-to-date they are meant to be kept. Currently http://clementgallet.github.io/libTAS/help/ doesn't seem to be linked from anywhere aside from the discord server.

[LukeSaward1]

This is unnecessary as people can just go to the website linked in the readme and go to the Documentation tab.

[clementgallet]

I wanted some documentation to be on GitHub pages, so that people could write and pull request doc. I'm pretty terrible at writing myself, even excluding the fact that it's not my native language.