Clarified how to update tests/test-helper.js when migrating ember-qunit to v5.x

[ijlee2]

Description

Currently, the README shows the following code snippet to help with upgrading ember-qunit to v5.x or above:

// tests/test-helper.js
import { setup } from 'qunit-dom';

//...

setup(QUnit.assert);

//...

I encountered the following error because I didn't import QUnit:

Global error: Uncaught ReferenceError: QUnit is not defined at http://localhost:7357/assets/tests.js

In this pull request, I updated the code snippet to show a developer (1) how they are to import QUnit and setup, and (2) in what recommended order they can call setup. I used QUnit DOM's own test helper to decide the recommended order.

[ijlee2]

I wasn't sure if it'd be good to show the default import statements,

import Application from 'my-project-name/app';
import config from 'my-project-name/config/environment';
import { setApplication } from '@ember/test-helpers';
import { start } from 'ember-qunit';

to make it even clearer where we get setApplication, Application, config, and start from.

I can push another commit to add these import statements if you'd like.

[Turbo87]

awesome, thanks! ❤️