DOC: add checklist to Pull Request Template

[tangkong]

Description

• Adds PR Checklist to PR Template
• adds pre-release notes for MNT: add TyphosDisplaySwitcher to positioner_row.ui #587

Motivation and Context

I forgor and didn't want to again

How Has This Been Tested?

N/A

Where Has This Been Documented?

This PR

Pre-merge checklist

• Code works interactively
• Code contains descriptive docstrings, including context and API
• New/changed functions and methods are covered in the test suite where possible
• Code has been checked for threading issues (no blocking tasks in GUI thread)
• Test suite passes locally
• Test suite passes on GitHub Actions
• Ran docs/pre-release-notes.sh and created a pre-release documentation page
• Pre-release docs include context, functional descriptions, and contributors as appropriate