Add check for developer's documentation

.github/PULL_REQUEST_TEMPLATE.md

@@ -15,4 +15,5 @@ The title of the PR must not reference an issue, because GitHub does not support
 - [ ] Tests created for changes (if applicable)
 - [ ] Manually tested changed features in running JabRef (always required)
 - [ ] Screenshots added in PR description (for UI changes)
+- [ ] [Checked developer's documentation](https://devdocs.jabref.org/): Is the information available and up to date? If not, I outlined it in this pull request.
 - [ ] [Checked documentation](https://docs.jabref.org/): Is the information available and up to date? If not, I created an issue at <https://github.com/JabRef/user-documentation/issues> or, even better, I submitted a pull request to the documentation repository.