Revise PR template. (#10774)

I recently revamped our cuDF [CONTRIBUTING guide](https://github.com/rapidsai/cudf/blob/HEAD/CONTRIBUTING.md). I would like to consider replacing the current PR template (which has a fairly daunting amount of text that is immediately deleted by many contributors) with a short checklist of actionable items and a reference to the CONTRIBUTING guide for longer content.

I kept this draft very minimal. Reviewers can see other examples here for inspiration: https://axolo.co/blog/p/part-3-github-pull-request-template. Happy to crowdsource others' thoughts here.

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - Lawrence Mitchell (https://github.com/wence-)
  - Jake Hemstad (https://github.com/jrhemstad)
  - Karthikeyan (https://github.com/karthikeyann)
  - AJ Schmidt (https://github.com/ajschmidt8)

URL: #10774

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,56 +1,9 @@
-<!--
-
-Thank you for contributing to cuDF :)
-
-Here are some guidelines to help the review process go smoothly.
-
-1. Please write a description in this text box of the changes that are being
-   made.
-
-2. Please ensure that you have written units tests for the changes made/features
-   added.
-
-3. There are CI checks in place to enforce that committed code follows our style
-   and syntax standards. Please see our contribution guide in `CONTRIBUTING.MD`
-   in the project root for more information about the checks we perform and how
-   you can run them locally.
-
-4. If you are closing an issue please use one of the automatic closing words as
-   noted here: https://help.github.com/articles/closing-issues-using-keywords/
-
-5. If your pull request is not ready for review but you want to make use of the
-   continuous integration testing facilities please mark your pull request as Draft.
-   https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/changing-the-stage-of-a-pull-request#converting-a-pull-request-to-a-draft
-
-6. If your pull request is ready to be reviewed without requiring additional
-   work on top of it, then remove it from "Draft" and make it "Ready for Review".
-   https://docs.github.com/en/github/collaborating-with-issues-and-pull-requests/changing-the-stage-of-a-pull-request#marking-a-pull-request-as-ready-for-review
-
-   If assistance is required to complete the functionality, for example when the
-   C/C++ code of a feature is complete but Python bindings are still required,
-   then add the label `help wanted` so that others can triage and assist.
-   The additional changes then can be implemented on top of the same PR.
-   If the assistance is done by members of the rapidsAI team, then no
-   additional actions are required by the creator of the original PR for this,
-   otherwise the original author of the PR needs to give permission to the
-   person(s) assisting to commit to their personal fork of the project. If that
-   doesn't happen then a new PR based on the code of the original PR can be
-   opened by the person assisting, which then will be the PR that will be
-   merged.
-
-7. Once all work has been done and review has taken place please do not add
-   features or make changes out of the scope of those requested by the reviewer
-   (doing this just add delays as already reviewed code ends up having to be
-   re-reviewed/it is hard to tell what is new etc!). Further, please do not
-   rebase your branch on the target branch, force push, or rewrite history.
-   Doing any of these causes the context of any comments made by reviewers to be lost.
-   If conflicts occur against the target branch they should be resolved by
-   merging the target branch into the branch used for making the pull request.
-
-8. Pull requests that modify cpp source that are marked ready for review 
-   will automatically be assigned two cudf-cpp-codeowners reviewers.
-   Ensure at least two approvals from cudf-cpp-codeowners before merging.
-
-Many thanks in advance for your cooperation!
-
--->
+## Description
+<!-- Provide a standalone description of changes in this PR. -->
+<!-- Reference any issues closed by this PR with "closes #1234". -->
+<!-- Note: The pull request title will be included in the CHANGELOG. -->
+
+## Checklist
+- [ ] I am familiar with the [Contributing Guidelines](https://github.com/rapidsai/cudf/blob/HEAD/CONTRIBUTING.md).
+- [ ] New or existing tests cover these changes.
+- [ ] The documentation is up to date with these changes.

CONTRIBUTING.md

@@ -34,7 +34,7 @@ conduct. More information can be found at:
    describes your planned work. For example, `fix-documentation`.
 5. Write code to address the issue or implement the feature.
 6. Add unit tests and unit benchmarks.
-7. [Create your pull request](https://github.com/rapidsai/cudf/compare).
+7. [Create your pull request](https://github.com/rapidsai/cudf/compare). To run continuous integration (CI) tests without requesting review, open a draft pull request.
 8. Verify that CI passes all [status checks](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/collaborating-on-repositories-with-code-quality-features/about-status-checks).
    Fix if needed.
 9. Wait for other developers to review your code and update code as needed.