Move developer guide from wiki to CONTRIBUTING.md

[probins]

as suggested in #2351 (comment)

Fixes #2351

Once this is merged, I can delete the wiki page. I don't think the wiki page is referred to from anywhere else on the website/repo

[probins]

I also corrected one minor typo I noticed

[bartvde]

Deleting the Wiki will probably lead to quite a few dead-ends Google searches? Can we put up a notice or something to guide people to the correct location(s)?

[probins]

good point. Yes, a temporary redirect would be a good idea

[ahocevar]

I wouldn't be worried about dead-end google searches. These go away pretty quickly.

[tschaub]

Thanks for the work on this @probins. This gives us a beast of a contributing doc. I've been going back/forth on whether I think this should be split up into multiple docs or not. At a minimum, I'd like to organize it so it is not so overwhelming for first time readers. I think this and other changes can be handled separately though.

[probins]

I have for the moment replaced the wiki page with a link to contributing.md

[ahocevar]

Good solution. Thanks @probins.