I think it would be nice if the Jenkins GitHub repository had a CONTRIBUTING.md file for when people want to commit new things to Jenkins, because a lot of repositories that I know of have one, and it would be useful to a lot of people if the Jenkins repository had a CONTRIBUTING.md file. Like I could possibly do it myself, but I don't know what I could put in it, especially since I'm a new commiter to Jenkins.
Is this really necessary? Many smaller OSS project may only have their Github repo, so for those it definitely makes sense. But Jenkins has a web site and wiki which clearly spell out how this works (Extend Jenkins -> Developing Jenkins -> Contributing to Jenkins). If you (abstract "you") can't be bothered to read that far, maybe you shouldn't open pull requests in the first place?