Update PULL_REQUEST_TEMPLATE.md

.github/PULL_REQUEST_TEMPLATE.md

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+**IMPORTANT: Do not submit PRs with only formatting / PEP8 / line length changes, I will close them with great prejudice.  The PEP8 checks I don't follow are intentional. PRs for minor bugfixes, typos, etc are fine.**
+
 # Summary
 
 e.g. This PR fixes ABC or adds the ability to do XYZ...