Add keyboard shortcuts

By using the `accesskey` attribute, we can specify a shortcut key for the user to activate or focus on an element. The value of the attribute has to be a single character.
It's worth noting that each browser provides a different combination of keys to access the shortcut.
Chrome`alt` + `ctrl` + key`alt` + key`alt` + key
Firefox`alt` + `ctrl` + key`alt` + `shift` + key`alt` + `shift` + key
Safari`alt` + `ctrl` + keyn/an/a
In the following sample code, pressing the combination `alt` + `ctrl` + `e` on Chrome macOS will trigger the button's `click` event.
<button accesskey="e" onclick="alert('Edit')">Edit</button>