[DOC] Add code example for renderSettled from @ember/renderer

Author: bertdeblock

packages/@ember/renderer/index.ts

@@ -12,15 +12,50 @@
   Returns a promise which will resolve when rendering has completed. In
   this context, rendering is completed when all auto-tracked state that is
   consumed in the template (including any tracked state in models, services,
-    etc.  that are then used in a template) has been updated in the DOM.
-
-    For example, in a test you might want to update some tracked state and
-    then run some assertions after rendering has completed. You _could_ use
-    `await settled()` in that location, but in some contexts you don't want to
-    wait for full settledness (which includes test waiters, pending AJAX/fetch,
-    run loops, etc) but instead only want to know when that updated value has
-    been rendered in the DOM. **THAT** is what `await renderSettled()` is _perfect_
-    for.
+  etc. that are then used in a template) has been updated in the DOM.
+
+  For example, in a test you might want to update some tracked state and
+  then run some assertions after rendering has completed. You _could_ use
+  `await settled()` in that location, but in some contexts you don't want to
+  wait for full settledness (which includes test waiters, pending AJAX/fetch,
+  run loops, etc) but instead only want to know when that updated value has
+  been rendered in the DOM. **THAT** is what `await renderSettled()` is
+  _perfect_ for.
+
+  ```js
+  import { renderSettled } from '@ember/renderer';
+  import { render } from '@ember/test-helpers';
+  import { tracked } from '@glimmer/tracking';
+  import { hbs } from 'ember-cli-htmlbars';
+  import { setupRenderingTest } from 'my-app/tests/helpers';
+  import { module, test } from 'qunit';
+
+  module('Integration | Component | profile-card', function (hooks) {
+    setupRenderingTest(hooks);
+
+    test("it renders the person's name", async function (assert) {
+      class Person {
+        @tracked name = '';
+      }
+
+      this.person = new Person();
+      this.person.name = 'John';
+
+      await render(hbs`
+        <ProfileCard @name={{this.person.name}} />
+      `);
+
+      assert.dom(this.element).hasText('John');
+
+      this.person.name = 'Jane';
+
+      await renderSettled(); // Wait until rendering has completed.
+
+      assert.dom(this.element).hasText('Jane');
+    });
+  });
+  ```
+
   @method renderSettled
   @returns {Promise<void>} a promise which fulfills when rendering has completed
   @public