Hotfix docs

Hotfix docs

While QtQuick 1 and 2 aren't clearly separated yet, some of the more
drastic differences (like the separate particle systems) need to be
explained a little in the interim. Or at least visible.

Change-Id: I60321bcb90a34730ed3e0862a049540ea36f8c5b
Reviewed-on: http://codereview.qt-project.org/5044
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Martin Jones <martin.jones@nokia.com>