How do I add hover text to main nav in Twenty Eleven

Site: https://marklindner.info/bbl/

I would like to add hover text, if possible, to my main navigation bar. Particularly to the BBL link on the nav bar. I want it to show ‘Beginner’s Beer Library” when it is hovered over.

Is this possible? How would I go about it. I do already have a child theme, I am using the Twenty Eleven Child with Sidebar Support v. 1.1 by Chris Aprea along with some modifications I have already successfully managed.

Thanks.