add a test for readme example

* which currently fails => need to update code..

jest.config.js

@@ -0,0 +1,4 @@
+module.exports = {
+  preset: "ts-jest",
+  testEnvironment: "jsdom",
+};

package.json

@@ -15,5 +15,8 @@
     "rollup-plugin-typescript2": "^0.29.0",
     "ts-jest": "^26.4.3",
     "typescript": "^4.0.5"
+  },
+  "scripts": {
+    "test": "jest"
   }
 }

src/LiveStorage.test.ts

@@ -0,0 +1,8 @@
+import { LiveStorage } from "./LiveStorage";
+
+test("REAME example does not throw", () => {
+  // TODO: BroadcastChannel is not available in Node 14 nor `jsdom` environment
+  const posts = new LiveStorage("posts", []);
+
+  posts.update((prevPosts) => prevPosts.concat({ title: "Brave new world" });
+});