Thanks for contributing to gVisor!

gVisor development happens on [Gerrit][gerrit] rather than GitHub, so we don't
accept pull requests here.

Please see the [contributing guidelines][contrib] for more information.

[contrib]: https://github.com/google/gvisor/blob/master/CONTRIBUTING.md
[gerrit]: https://gvisor-review.googlesource.com

Add a GitHub pull request template.
Add a GitHub pull request template.

It directs users to our contributor guidelines and Gerrit instance.

PiperOrigin-RevId: 194830523
Change-Id: I9882da0e95d04f7e1ee941bf65d40fbe45a47b24
