update doc for pub&sub.
update doc for pub&sub.

you can only use the session bus for context kit layer.

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