Add info on how to run tests

Author: Noratrieb

terragrunt/modules/release-distribution/lambdas/doc-router/test.mjs

@@ -1,3 +1,7 @@
+// A test that asserts that the redirects work correctly.
+// It can be run with
+// node --test test.mjs
+
 import { test } from "node:test";
 import assert from "node:assert";
 import lambda from "./index.js";