Following installation guide here.
$ cd docs
$ bundle exec jekyll serve
If you see the error Liquid Exception: undefined method untaint' for "Welcome to Jekyll!":String in /_layouts/post.html jekyll 3.9.2 | Error: undefined method untaint' for "Welcome to Jekyll!":String,
you might need to update gem github-pages to make use of liquid-4.0.4 which is already in Gemfile. Run the ff and test again.
$ bundle update github-pages