docs(aio): add NgModule docs (#20306)

PR Close #20306

aio/content/examples/feature-modules/e2e/app.e2e-spec.ts

@@ -0,0 +1,17 @@
+import { AppPage } from './app.po';
+
+describe('feature-modules App', () => {
+  let page: AppPage;
+
+  beforeEach(() => {
+    page = new AppPage();
+  });
+
+  it('should display message saying app works', () => {
+    page.navigateTo();
+    expect(page.getParagraphText()).toEqual('app works!');
+  });
+});
+
+
+