Write tutorial for Wechaty new developers.

[huan]

There is three tutorial type we can select:

1. Essentials tutorial: a "top-down" tutorial that teaches how to use Wechaty the right way, using our latest recommended APIs and best practices.
2. The Basic tutorial and Advanced tutorial are a "bottom-up" tutorial that teaches how Wechaty works, starting from first principles.

• The concept is borrowing from Redux:
  1. Redux Essentials
  2. Basics
  3. Advanced

The tutorial can be published as our blog post at https://wechaty.js.org at first, and then we can continue editing them and try to make them better so that it can be published as an official document at https://wechaty.js.org/docs/.

[lijiarui]

link this: https://github.com/wechaty/wechaty.js.org/issues/430