The image is designed to behave like GitHub Pages, it utilizes the latest version of the Ruby gem "github-pages" which is maintained by GitHub. But it also includes some nice tools and utilities that aren't necessarily supported by GitHub pages, which runs in safe mode, with only a limited support for plugins.
The source is available at GitHub from lakruzz/jekyll-plus
To build/serve a jekyll site change directory into the root of your jekyll site folder and then run jekyll serve
as exemplified.
Mac - using Docker-machine "default"
docker run -i -t --rm \
-v $(pwd):/app:rw \
--workdir /app \
-p 80:4000 lakruzz/jekyll-plus \
jekyll serve --host 0.0.0.0 --force_polling
Now browse the IP of your docker machine ("default" used in the example):
open http://`docker-machine ip default`
Linux
docker run -i -t --rm \
-v $(pwd):/app:rw \
--workdir /app \
-p 4000:4000 lakruzz/jekyll-plus \
jekyll serve
Now browse port 4000 on you localhost:
xdg-open localhost:4000
Use the issues on the GitHub repo: lakruzz/jekyll-plus
There the answered support issues are marked "Q&A - Asked and Answered"
...read my blogpost Docker Jekyll - 5 easy steps