I think we should write a Contribution Guide from which:

1. New comers know how they can contribute
2. Everyone know what do the community, especially users and readers expect
3. Most importantly, everyone learns about the standard of code contribution, like do we need testing in submission? Is it a strict requirement? Do we need comment description? Are one-liners acceptable? How to deal with "one-liner" alternatives?

I found #432 and #433 relating to this, but the commit concerned is not quite tailor-made to us and thus reading it will not help a newcomer to know points 2 and 3.