I want to design forum just like this one. Any advise on how to go about it?
What do you mean by "design"? Do you mean setup your own Spirit instance in some host/VPS/cloud?
Yes, is there a documentation that I can use to set this up?
No, there is not. If you know how to deploy a Django project, then you know how to deploy Spirit. There are plenty of tutorials out there for every possible cloud/VPS/hosting. The local installation instructions is all there is, and all you should need to get started.
That said, if all you want is to push a button and get Spirit deployed, then try spirit-heroku. I believe that still works. Heroku is pretty expensive, though, but you can try it for free.