add new demo pic [skip ci]
add new demo pic [skip ci]

tipunch74/MaterialDesignInXamlToolkit,ButchersBoy/MaterialDesignInXamlToolkit,ButchersBoy/MaterialDesignInXamlToolkit,tipunch74/MaterialDesignInXamlToolkit,ButchersBoy/MaterialDesignInXamlToolkit,tipunch74/MaterialDesignInXamlToolkit,DingpingZhang/MaterialDesignInXamlToolkit