Running locally can be done with Jekyll. Follow setup instructions at https://help.github.com/en/articles/setting-up-your-github-pages-site-locally-with-jekyll
Run
docs$ bundle exec jekyll serve
Another way to do local development without doing the Ruby setup steps is to use a docker container:
$ docker run -it --rm -v "$PWD":/usr/src/app -p "4000:4000" starefossen/github-pages