PULL_REQUEST_TEMPLATE.md

What do these changes do?

• commit message follows format outlined here
• passes flake8 modin/ asv_bench/benchmarks scripts/doc_checker.py
• passes black --check modin/ asv_bench/benchmarks scripts/doc_checker.py
• signed commit with git commit -s
• Resolves #?
• tests added and passing
• module layout described at docs/development/architecture.rst is up-to-date
• added (Issue Number: PR title (PR Number)) and github username to release notes for next major release