If the CONTRIBUTING[.md] file exists, Github will show a link to it to
anyone who files an issue on Github or opens a pull request on
Github. We don't want people to do that, so this file points people at
the OpenStack wiki page with instructions on how to contribute
properly. This should cut down on the number of pull requests and
Github issues that we then have to spend our valuable time ignoring.
See also <https://github.com/blog/1184-contributing-guidelines>.