I have seen a relatively large number of pull requests via the Github mirror repository, because would-be contributors presumably just look on Github and, having found Python there, assume this is the place for contributions. The standard README file gives no clue that the Github repository should not be used as the basis for contributory pull requests, and neither should it. Fortunately Github will display a README.md file in preference to REAMDE when one is found. This patch adds a message, highly visible to Github users, that they are in the wrong place. For an indication of how the Github page will then look, visit https://github.com/holdenweb/python/tree/README where the patch is already installed.
I don't seem to be able to activate the PR template, but if you are happy it works then I guess this would be a belt-and-braces change. If nobody merges it and it gets closed that's fine, but if it obviates just a few pull requests it will save both the core devs and the contributors some time.