Add PR checklist template

[rowanhemsi]

Is your feature request related to a problem? Please describe.
As a developer/reviewer, I want to easily see what standards I should meet when submitting a pull request

Describe the solution you'd like
Add a PR template to use with all new pull requests

Describe alternatives you've considered
The contributing guidance could be updated instead of or in addition to adding a review template, but this would require contributors and reviewers to go looking for the standards when developing new features.

Additional context
Example checklists can be found in the Duck Book or other recent projects