Docs: Delete placeholder to use top-level file (#23869)
Summary:
Replaces and closes https://github.com/pytorch/pytorch/issues/23864.
When opening a pull request, GitHub shows you this:
Or this:
However, that links to https://github.com/pytorch/pytorch/blob/master/.github/CONTRIBUTING.md which looks like:
As the commit message shows, that was a placeholder. There's already a real `CONTRIBUTING.md` document, so *delete the placeholder*.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23869
Differential Revision: D16667966
Pulled By: ezyang
fbshipit-source-id: c4135ebbb75de803ef227e4608e16da1a2e83a0c
