A series of walkthrough tutorials to help everyone to better understand the system

[yatli]

I think it is better that we maintain both a (unordered) set of rather complete examples, and a (linear) series of tutorials, each covering a very specific topic of our system. A new user can go through them one by one and then get a better understanding of the system, compared to looking at examples, which are more task-oriented.

Of course, if we design it "incremental learning" oriented, at some stages one can reach a checkpoint where a rather complete example can be introduced.

@leoxia @shaobin thoughts?