Add section about testing UIKit interaction with Quick.

Hello,

I've been using Quick for unit testing view controllers. I saw issue #39 requested a section about UIKit testing, so I thought I'd write something up. Let me know if you'd like any changes. There is a reference application implementing the Swift example tests (and code to make the tests pass) located here: [Reference Swift Application](https://github.com/sidraval/DolphinTableViewApp).
Rather than calling `viewDidLoad` directly, I usually access the view, which itself triggers methods like `viewDidLoad`:

```swift
beforeEach {
  viewController = DolphinTableViewController()
  viewController.view
}
```

I'd also add a short comment explaining why we're triggering a view load.