Add GH actions for deploy

[AgustinRamiroDiaz]

While reading the README I found that the GitHub Pages link is outdated.

I'm proposing this action to keep the gh-pages branch up to date

A demo for this can be seen with my fork at https://agustinramirodiaz.github.io/eleventy-base-blog/

This might require some configuration in the repo's settings->actions->Workflow permissions:

• give GITHUB_TOKEN read and write permissions

Credits to the inspiration