Doc change: Add additional chromium flags

[mhellmeier]

The documentation suggests adding the following lines to allow a kiosk mode at startup with the chromium browser:

@xset s off
@xset -dpms
@xset s noblank
@chromium-browser --incognito --kiosk http://localhost/

When using the application with a touchscreen, two problems appear:
First, the chromium browser allows swiping left and right to go to the previous or next page. This results in some click point errors in the gallery. I would suggest adding the following flag to disable this feature: --overscroll-history-navigation=0.

Second, the error message Can not update Chromium appears after some time. This is a known bug on Raspbian (see this SO question). I would suggest adding the --disable-component-update flag and follow the workaround describes here.

Together, this results in the following: @chromium-browser --incognito --overscroll-history-navigation=0 --disable-component-update --kiosk http://localhost/

[mhellmeier]

It is also useful to add the --disable-pinch flag to disable zoom events.