Update HildonPickerDialog documentation
Update HildonPickerDialog documentation

Explain that the dialog emits GtkDialog::response when a selection is
completed

archlinuxarm-n900/libhildon,archlinuxarm-n900/libhildon,community-ssu/hildon,archlinuxarm-n900/libhildon,community-ssu/hildon,community-ssu/hildon