[Vv] Qt5 from git

[David Boersma]

Hi!

I think that the QT part of the installation instructions may need some 
updates. The "git clone" command as currently given will *not* yield 
Qt5, but the latest 4.* tag instead. If the intention is to let the user 
install the latest greatest Qt5 then the clone command should be like this:

git clone git://code.qt.io/qt/qt5.git

And it should be followed by "cd qt5 && ./init-repository" before 
running "./configure". It looks like the "-no-gtkstyle" option is no 
longer recognized.