GUI: at least mention that other people are involved in Trojitá as well

This is far from a perfect fix, but I simply wasn't able to make QMessageBox
recognize <a> elements -- they are "recognized" and redered properly, but they
do not react to mouse clicks even after following vairous advices [1] [2].

[1] http://www.qtcentre.org/threads/17365-Clickable-URL-in-QMessageBox
[2] http://stackoverflow.com/questions/10028608/qmessagebox-with-link-inside-unable-to-click