Added navigation within lightbox

You can have links inside the lightbox to navigate to another url, without closing the lightbox.
In order to do that, you only have to add the links to navigate inside the content of the lighbox, with the class js-lightbox-navigation These links will open the url in the href in the lightbox
I feel like this would read better as

> In order to do that, add the links within the content of the ligthbox and give them the `js-lightbox-navigation` class with the `href` pointing to the url to load.