The first version of pull request template

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

Author: weihanglo

.github/PULL_REQUEST_TEMPLATE.md

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+<!--
+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.
+
+Please DELETE all these comments before submitting the PR.
+-->
+
+### What this PR tries 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 to 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, suck as prior arts,
+future extensions, an unresolved problem, or a TODO list.
+-->