Add Github Action workflow to automate deployment of documentation

[1player]

Fixes #25 and it is a good starting point for #24

[hugopl]

How does it works? it create commits on gh-pages branche?

[1player]

Yes, it uses the peaceiris/actions-gh-pages@v3 action which seems to be the most used one. I've ran it on my repo, you can check the result here: 1player@bdb690a or 1player@a0f661d

(for some reason Github is having issues rendering that commit, just have a look at my gh-pages branch)

Basically that action recreates the docs directory from scratch and commits it, with the master commit it's referring to in the name. Pretty neat.