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

Author: bors

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,36 @@
+<!--
+Thanks for submitting a pull request 🎉! Here are some tips for you:
+
+* If this is your first contribution, read "Cargo Contribution Guide":
+  https://doc.crates.io/contrib/
+* Run `cargo fmt --all` to format your code changes.
+* Small commits and pull requests are always preferable and easy to review.
+* If your idea is large and needs feedback from the community, read how:
+  https://doc.crates.io/contrib/process/#working-on-large-features
+* Cargo takes care of compatibility. Read our design principles:
+  https://doc.crates.io/contrib/design.html
+* When changing help text of cargo commands, follow the steps to generate docs:
+  https://github.com/rust-lang/cargo/tree/master/src/doc#building-the-man-pages
+* If your PR is not finished, set it as "draft" PR or add "WIP" in its title.
+* It's ok to use the CI resources to test your PR, but please don't abuse them.
+
+### What does this PR try to resolve?
+
+Explain the motivation behind this change.
+A clear overview along with an in-depth explanation are helpful.
+
+You can use `Fixes #<issue number>` to associate this PR to an existing issue.
+
+### How should we test and review this PR?
+
+Demonstrate how you test this change and guide reviewers through your PR.
+With a smooth review process, a pull request usually gets reviewed quicker.
+
+If you don't know how to write and run your tests, please read the guide:
+https://doc.crates.io/contrib/tests
+
+### Additional information
+
+Other information you want to mention in this PR, such as prior arts,
+future extensions, an unresolved problem, or a TODO list.
+-->