fix syntax errors and split the create a rails app section into a seperate page for docker

[CZagrobelny]

1. Fix spelling and syntax errors on sites/en/installfest/docker.step
2. The Create a Rails App section diverges dramatically for Docker and non-Docker users, so I split the Docker Create a Rails App docs into their own page.
3. Small change to clarify instructions for Docker users and make them consistent: sites/en/installfest/deploy_a_rails_app.step