chore: Add a Pull Request template / checklist (#94)

* Add Pull Request template
* Update the changelog

Author: bgrant

CHANGELOG.md

@@ -7,6 +7,7 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 
 # [unreleased] - YYYY-MM-DD
 ### Added
+- [PR 94](https://github.com/salesforce/django-declarative-apis/pull/94) Add a Pull Request template/checklist to the repo
 - [PR 92](https://github.com/salesforce/django-declarative-apis/pull/92) Run tests and static analysis as a PR check using GitHub actions
 - [PR 83](https://github.com/salesforce/django-declarative-apis/pull/83) Allow Django 3
 - [PR 82](https://github.com/salesforce/django-declarative-apis/pull/82) Allow Celery 5 by using `shared_task`

pull_request_template.md

@@ -0,0 +1,6 @@
+- [ ] Update CHANGELOG.md
+- [ ] Update README.md (as needed)
+- [ ] New dependencies were added to `requirements.txt` or `requirements-dev.txt`
+- [ ] `pip install` succeeds with a clean virtualenv
+- [ ] There are new or modified tests that cover changes
+- [ ] Test coverage is maintained or expanded