Fix bug in events.js

[clairefro]

Current boiler runs all the exercise code blocks on page load, giving away the point of the exercise.

Instead, commented out the code blocks be default so students can see the effect of adding event listeners

[clairefro]

One more important fix - the old boiler code suggested selecting the fourth div card and adding a keydown and keyup event, however keyboard events only work on input, textarea etc elements then bubble up to the document. The event does not fire when the listener is placed on the div.

https://developer.mozilla.org/en-US/docs/Web/API/Element/keydown_event

So instead, in the last commit, I suggested removing the part where you save the fourth card to a variable, and instead have students just add an event listener to the document in order for the event to fire properly

ex:

document.addEventListener('keydown', function() {
    // do something cool
})
``