feat: Added PR template

[Alex-Zughaid]

Linked Issues

Closes #1457

Description of Changes

Added PULL_REQUEST_TEMPLATE.md

Reviewer Guide

Feel free to give any thoughts on whether this is needed or suggest anything that is missing

Checklist

• lake build passes
• Check if AI was used to write the majority of this PR
• New definitions have docstrings

Additional Comments

n/a

[github-actions]

Thank you for this PR, which will now be reviewed. If submitting to ./Physlib or ./QuantumInfo, please see our review guidelines if you are not familiar with the process. You should expect a back and forth with a reviewer before your PR is merged. See also that link for how to add appropriate labels to your PR. The PR will also go through a number of automated checks. You can learn more about these here, including how to run them locally.

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