Add a checklist item to update the roadmap board (#321)

Author: lfrancke

template/.github/pull_request_template.md

@@ -32,4 +32,5 @@
 # Acceptance
 - [ ] Feature Tracker has been updated
 - [ ] Proper release label has been added
+- [ ] [Roadmap](https://github.com/orgs/stackabletech/projects/25/views/1) has been updated
 ```