Document mobilityconfig.prf usage
Document mobilityconfig.prf usage

Task-number: QTMOBILITY-1406
(cherry picked from commit 6658209c7dcaad472cb3b0f631f1811b2fe2d166)

enthought/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,KDE/android-qt-mobility,enthought/qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility,KDE/android-qt-mobility,tmcguire/qt-mobility,qtproject/qt-mobility,qtproject/qt-mobility,tmcguire/qt-mobility,KDE/android-qt-mobility,KDE/android-qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility