docs: require users to disclose in PR whether an A/LLM tool is used

Add disclosure section for AI tool usage in PRs.

.github/PULL_REQUEST_TEMPLATE.md

@@ -15,3 +15,9 @@ This PR fixes
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+## Disclosure
+<!-- **Important:** Due to the way LLMs work, we require you to disclose the fact, if you have contributed to them, so that we can take care of that fact when reviewing your work. Please note that, especially as a first-time contributor, **you must explictly mention** if you have _not_ used an AI tool, as we want to limit spam PRs. -->
+* [x] I do have used an AI/LLM tool for the work in this PR.
+* [ ] I have **not** used an AI/LLM tool for the work in this PR.
+