Document what is required to build Qt on a Linux system

The naive approach to building Qt ("Let's install the X11-development packages -> ready-set-go") on a Vanilla (say) Kubuntu system leads to broken painting and fonts. This is because the development packages of some libraries are required on top of x11-dev, for example XRandr and Xfixes.
Also, getting phonon to work requires some gstreamer development packages.

The sure-fire approach to get this working is to install the KDE 4 development packages, but that might be too much.

I suggest ask a knowledgeable person (Jens Bache-Wig or Brad) and add a paragraph containing a list of libraries/development packages.