Auto merge of #10218 - weihanglo:pr-template, r=alexcrichton

The first version of pull request template

### What this PR tries to resolve?

We're trying to extract information out off the head of contributors.
Hope this help the review process more friendly for everyone.

### How to test and review this PR?

Copy this template and paste to your GitHub Web UI to see if it renders well.

### Additional information

Kubernetes community has one of the best guide of ["Best Practices for Faster Reviews"].
It describes tips for contributors tocreate a high quality PR. We might want
to create our own one and include it in PR template in the future.

In addition, I don't know how much time it take to update the changelog. I saw
some projects let PR author write down the release note of the PR. This sounds
helpful to take some burden off from maintainers, as well as let contributors
feel more involved. Anyway, it's not in this PR but is good to discuss later.

["Best Practices for Faster Reviews"]: https://github.com/kubernetes/community/blob/9b38b270640009f28d7d8710f74d955e0c374cef/contributors/guide/pull-requests.md#best-practices-for-faster-reviews