Establish guidelines for usage of AI in PRs

.github/PULL_REQUEST_TEMPLATE.md

@@ -13,6 +13,7 @@ Don't reference an issue in the PR title because GitHub does not support auto-li
 - [x] done; [ ] not done / not applicable
 -->
 
+- [x] I own the copyright of the code submitted and I licence it under the [MIT license](https://github.com/JabRef/jabref/blob/main/LICENSE)
 - [ ] Change in `CHANGELOG.md` described in a way that is understandable for the average user (if applicable)
 - [ ] Tests created for changes (if applicable)
 - [ ] Manually tested changed features in running JabRef (always required)

CONTRIBUTING.md

@@ -113,6 +113,17 @@ We also show all contributors in our blog posts. See [Release 5.15 blog post](ht
 
 Your contribution is considered being made under [MIT license](https://tldrlegal.com/license/mit-license).
 
+#### Notes on AI usage
+
+Please keep these two principles in mind when you contribute:
+
+1. Never let an LLM speak for you.
+2. Never let an LLM think for you.
+
+More reading on that is available at <https://roe.dev/blog/using-ai-in-open-source>.
+
+We reserve the right to reject pull requests that contain little or no genuine and original contribution from the contributor.
+
 ### Development hints
 
 #### When adding an external dependency