@HanchaiN can you have a look at this improved CONTRIBUTING.md?

Thinking about it, maybe it is better to keep CONTRIBUTING.md concise, and put the extensive documentation in README.md instead. Then we can link from CONTRIBUTING.md to these sections in README.md. What do you think?

I think that the description is clear enough for new contributors (else they will raise the issue again sometime).
Whether or not the documentation is seperated depends on you. As long as they can reach the infomation from where they might look for them, that's fine.

For what it's worth, the new CONTRIBUTING in this PR seems clear enough but not too long. I would recommend (as part of this PR) mentioning the CONTRIBUTING guide in the README, though -- not all potential contributors look at the whole file tree (speaking from experience), but I think it's pretty common to at least read the README.

I've moved the explanation on implementing a new function to the README, and add a small FAQ section to CONTRIBUTING.md linking to this section to keep it short.

I'll merge this PR now, thanks for the feedback.