We have got a lot of requests concerning continuous integration lately. That's why we've published a new general article in our docs on how to integrate CI in your fortrabbit workflow. Pieter from wercker also just published this great article on how to integrate fortrabbit with wercker. Here is another one from us on how you could something similar combining Codeship with fortrabbit.
They walk you through the full process with a freshly created Fortrabbit application so you can see how to get it set from the start. The article shows you how to set up Codeship with the repository provider and the callback for push notifications. You'll have to set up a ssh key for Codeship to be able to access the repository and a special script that happens on push to trigger the build. There's also a bit at the end about "going multistage" with a different deployment process for each branch.