title: How to observe text change in UITextField using RxSwift?
body: <p>I want to observe any change of the <code>UITextField.text</code> property using RxSwift.</p>
  
  <p>I trying to use <code>rx.text</code> property, but it called only when I set <code>text</code> property like this: <code>textField.text = ""</code>, but not working when I typing text.</p>
  
  <p>Also I tried to use <code>rx.observe(String.self, "text")</code>, but it gives the same result.</p>
  
  <p>How can I observe any change of the text in UITextField?</p>