Show a tooltip for the repo link button

The popup for this button was removed earlier for being uninformative, but
we do need this for the survey period where the button texts are hidden.

Change-Id: I451a6bf9cf3c28fbc11f7094db1e7aa86eb87cd7
Mingle: https://wikimedia.mingle.thoughtworks.com/projects/multimedia/cards/226
Merge "Show a tooltip for the repo link button"