working on small enhancements

I have made a few changes.

The target is to add a section for building PySide on OS X.

I would like to add my homebrew installation, because that is minimalistic
and avoids building QT.

Before that, I'd like to modify the subsections slightly, so the name of the current OS
is always visible from the section header. Having the same subtitle multiple times
is confusing for me (bad vision). Is that ok?