Configure where to put the dependencies, here in a subdirectory 'vendor/bundle' in the current directory:
bundle config set --local path 'vendor/bundle'
Fetch and install the dependencies:
$ bundle install
Then you can build and run the development web server:
$ bundle exec jekyll serve
The website can be accessed at http://localhost:4000 and the development server will watch the directory for changes and rebuild.
_data/navigation.yml
defines the menu