You are right that it is gone (hidden) at the moment, and we definitely forgot to hide the docs.
We have some internal discussion right now about what to do with this project, in meantime, you can use my personal fork https://github.com/buger/tyk_quickstart.
Thing is that people was using quickstart for performance evaluation and for some production installations, ignoring all the warnings, so we decided to hide it temporarily until we find a better solution. For example some interactive tutorial on our site or similar.
Apologies for the confusion.