Update CONTRIBUTING.md

Author: peterdotjs

CONTRIBUTING.md

@@ -15,8 +15,9 @@ We actively welcome your pull requests.
 1. Fork the repo and create your branch from `master`.
 2. If you've added code that should be tested, add tests.
 3. If you've changed APIs, update the documentation.
-4. Ensure the test suite passes.
-5. If you haven't already, complete the Contributor License Agreement ("CLA").
+4. If you've updated/added a UI component, please add a screenshot.
+5. Ensure the test suite passes.
+6. If you haven't already, complete the Contributor License Agreement ("CLA").
 
 ## Contributor License Agreement ("CLA")
 In order to accept your pull request, we need you to submit a CLA. You only need