ci(danger): add dangerjs for GitHub

Add GitHub workflow for running dangerjs on pull requests.
Add GitHub layout for DangerJS.

.github/dangerjs/prDescription.ts

@@ -0,0 +1,19 @@
+import { DangerDSLType, DangerResults } from "danger";
+declare const danger: DangerDSLType;
+declare const warn: (message: string, results?: DangerResults) => void;
+
+/**
+ * Check if pull request has has a sufficiently accurate description
+ *
+ * @dangerjs WARN
+ */
+export default function (): void {
+    const prDescription: string = danger.github.pr.body;
+    const shortPrDescriptionThreshold: number = 100; // Description is considered too short below this number of characters
+
+    if (prDescription.length < shortPrDescriptionThreshold) {
+        return warn(
+            "The PR description looks very brief, please check if more details can be added."
+        );
+    }
+}