Add notes about using prova.py and the pyqt widget with the xw??.py examples.
Add notes about using prova.py and the pyqt widget with the xw??.py examples.

svn path=/trunk/; revision=3293

FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot,FreeScienceCommunity/PLPlot