Added another accessible modal window link

Adding the awesome pen by @scottaohara linked from this article: http://www.smashingmagazine.com/2014/09/15/making-modal-windows-better-for-everyone/
Merge branch 'patch-14' of github.com:svinkle/a11yproject.com into svinkle-patch-14

* 'patch-14' of github.com:svinkle/a11yproject.com:
  Added another accessible modal window link
Merge branch 'svinkle-patch-14' into gh-pages

* svinkle-patch-14:
  Added another accessible modal window link

t push origin gh-pages# Lines starting with '#' will be ignored, and an empty message aborts