Add PR template (#2556)

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
+- [ ] This PR targets the correct branch (`main` for normal development, `v3-support` for v3 support)
+
+### 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.
+  - Describe how you used it (e.g., by pasting your prompt):