Use a better example for Effect hook

The following example is used in:

• https://reactjs.org/docs/hooks-overview.html#effect-hook
• https://reactjs.org/docs/hooks-effect.html

import React, { useState, useEffect } from 'react';

function Example() {
  const [count, setCount] = useState(0);

  // Similar to componentDidMount and componentDidUpdate:
  useEffect(() => {
    // Update the document title using the browser API
    document.title = `You clicked ${count} times`;
  });

  return (
    <div>
      <p>You clicked {count} times</p>
      <button onClick={() => setCount(count + 1)}>
        Click me
      </button>
    </div>
  );
}

This example creates confusion because the example doesn't actually need useEffect to operate correctly.

If you set document.title outside of the useEffect, the app behaves exactly the same.

Suggested changes

• Use an example which would not work correctly if it wasn't placed in a useEffect. It should be something that depends on the DOM having been updated. Maybe setting the document.title to a document.getElementById or something like that. This would also be a contrived/useless example. Something practical would be better.

• Show the lifecycle of useEffect early. I was most interested in the lifecycle of when this method is called. In Dan's recent blog post on effects, this is the first thing that is covered, and it should be the same for these docs.

Comienza con los ejemplos de Effect Hook en hooks-overview.html#effect-hook y hooks-effect.html, y luego compara el ejemplo actual con la explicación del ciclo de vida en la documentación referenciada. Sustituye el ejemplo confuso por uno que demuestre por qué se necesita useEffect e introduce su ciclo de vida antes; se considerará terminado cuando ambas páginas expliquen el comportamiento de forma coherente y muestren el ejemplo mejorado.