Get a shell into the container

docker run --rm -it -w $PWD -v $PWD:$PWD -p4000:4000 -p35729:35729 jekyll/jekyll bash

bundle the gems in the Gemfile

bundle

Run jekyll

jekyll serve -w --drafts --config _config.yml,_config-dev.yml

In a separate terminal, open the browser to the site

open http://localhost:4000