Add changelog entries to PR template

.github/pull_request_template.md

@@ -5,6 +5,7 @@
 * [ ] I used the [`pre-commit` hook](https://precice.org/dev-docs-dev-tooling.html#setting-up-pre-commit) and used `pre-commit run --all` to apply all available hooks.
 * [ ] I added a test to cover the proposed changes in our test suite.
 * [ ] I updated the documentation in `docs/README.md`.
+* [ ] I added a changelog entry in `./changelog-entries/` (create if necessary).
 * [ ] I updated potential breaking changes in the tutorial [`precice/tutorials/aste-turbine`](https://github.com/precice/tutorials/tree/develop/aste-turbine).
 
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