Download or clone into ~/.middleman/boilerplate:
$ git clone git@github.com:droidlabs/middleman-boilerplate.git ~/.middleman/boilerplate
Install middleman:
gem install middleman
Initialize a new middleman project:
$ middleman init my_project --template=boilerplate
Then bundle, and start the middleman server:
middleman
You can read more about project templates on the Middleman site.