Create workout to cover the event loop in JS

[lizTheDeveloper]

We need a workout that covers the following objective:

• Explain the event loop in JavaScript

This means users should be able to explain how the event loop works- when are functions added to the stack, when do they get run, when are they garbage collected, etc.

We don't have materials that explain the event loop in JavaScript. This is clearly deeper material, so it'll go in the last section of JavaScript.