[docs] Add "Contribute Code" community documentation

[caozhen1937]

Purpose

Linked issue: close #535

[CLAassistant]

All committers have signed the CLA.

[caozhen1937]

Hi, @wuchong , I have a few questions. Please help me answer them.

1. How to debug the preview of html format code?
2. The current commit incorporates only the information that I think is important. There is also a lot of information that can be presented separately, such as the PR process, Code Style and Quality Guide. Maybe current phase should be simpler.
3. debug failed cases, I didn't think of a good way to explain it, except for screenshots

[wuchong]

Hi @caozhen1937, it appears that the CLA has not been signed. This is likely because the username or email in the commit information does not match your GitHub account. Could you please verify whether the commit is using an incorrect email or if the email used in the commit is not registered to your GitHub account?

[caozhen1937]

@wuchong ,CLA check passed. I changed my email, thank you.

[wuchong]

@caozhen1937 Thanks for the contribution. LGTM.