Added hint for building on Fedora (qmake versions)

On Fedora you have:
qmake (Qt 3)
qmake-qt4 (Qt 4)
qmake-qt5 (Qt 5)
So using `qmake` does not work since qupzilla is designed for Qt4/Qt5.
Merge pull request #1021 from genodeftest/patch-1

Added hint for building on Fedora (qmake versions)