Update anchor tag with required "data-reveal"

As described here:
http://foundation.zurb.com/forum/posts/258-reveal-problem-with-foundation-5
"data-reveal" is required to have reveal plugin working properly. This example works nice as is but if you have your buttons (anchors) loaded with jQuery (DOM update after document ready) it will not work.
Let's save devs time with this tip in the documentation.
Thanks!
Merge pull request #4156 from tuxone/patch-1

Update anchor tag with required "data-reveal"