Add PR template

Author: VeckoTheGecko

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,14 @@
+<!-- Feel free to remove check-list items aren't relevant to your change -->
+
+- [ ] Closes #xxxx
+- [ ] Tests added
+
+### AI Disclosure
+
+<!--- Please review our AI & contribution guidelines (https://docs.oceanparcels.org/en/main/development/policies.html#use-of-ai-in-development). Remove this section if your PR does not contain AI-generated content. --->
+
+- [ ] This PR contains AI-generated content.
+  - [ ] I have tested any AI-generated content in my PR.
+  - [ ] I take responsibility for any AI-generated content in my PR.
+    <!--- If you used AI to generate code, please specify the tool used and the prompt below. --->
+    Tools: {e.g., Claude, Codex, GitHub Copilot, ChatGPT, etc.}