Looks like you don't have rake installed. I was assuming that you have bundler and rake installed already (as per readme). What's the output of `gem list`? Try `gem install bundler rake`.

An alternative, if you feel a bit adventurous is to use Docker. You could try to checkout this branch of hibernate.org - https://github.com/hferentschik/hibernate.org/tree/build-simplify. Change into the .docker directory and run:

docker build -t fedora/hibernate.org .
docker run -t -i -p 4242:4242 -v `pwd | xargs dirname`:/home/dev/hibernate.org fedora/hibernate.org 

This way all the awestruct setup is handled by the container. So you can run `rake preview` in the container. At the same time you can keep editing your sources locally. Obviously this requires Docker to be installed and some familiarity with it.