should re-organize, update the docs as complete as possible

[hoatle]

docs is really really important for the project, we must make sure new devs can follow steps by steps easily, can understand and master teracy-dev from the provided docs:

• getting started
• basic usage (by use cases, examples)
• advanced usage (by use cases, examples)
• reference guide (provided APIs, features to look up)
• developer guide (so that devs can follow and contribute to the project)
• anything else?

[hoatle]

interesting related: https://medium.com/@mikeal/docs-docs-docs-1e06d17fa06f

[hoatle]

@phuonglm @hoavt please provide the docs outline in details (topic by topic) here and I will verify to approve.

[hoatle]

should learn from this https://developers.google.com/style/ (thanks to @phuonglm)