Add Danger.js

dangerfile.js

@@ -0,0 +1,9 @@
+import { message, danger } from "danger"
+
+// Add a CHANGELOG entry for app changes
+const hasChangelog = includes(danger.git.modified_files, "CHANGELOG.md")
+const isTrivial = contains((danger.github.pr.body + danger.github.pr.title), "#trivial")
+
+if (!hasChangelog && !isTrivial) {
+    warn("Please add a `CHANGELOG.md` entry for your changes.")
+}