Add new lint checklist

Author: oli-obk

.github/PULL_REQUEST_TEMPLATE

@@ -10,6 +10,15 @@ If your PR fixes an issue, you can add "fixes #issue_number" into this
 PR description. This way the issue will be automatically closed when
 your PR is merged.
 
+If you added a new lint, here's a checklist for things that will be
+checked during review or continuous integration.
+
+- [ ] Followed [lint naming conventions][lint_naming]
+- [ ] Added passing UI tests (including committed `.stderr` file)
+- [ ] `cargo test` passes locally
+- [ ] Executed `util/dev update_lints`
+- [ ] Added lint documentation
+
 Delete this line and everything above before opening your PR -->
 
 changelog: none