bits() and constBits() could mention padding bytes due to alignment

scanLine() has a note about alignment:
https://doc.qt.io/qt-5/qimage.html#scanLine

This could be added to bits() and constBits() too that currently don't say much:
https://doc.qt.io/qt-5/qimage.html#bits

This can lead to surprises if one assumes it contains continuous pixel data.