docs/advanced: add example how to mount the correct data partition in a redundant data layout
docs/advanced: add example how to mount the correct data partition in a redundant data layout

Signed-off-by: Fabian Knapp <e9accd498fb2e3165dbc9d026755c2284b471e3d@ambibox.de>

rauc/rauc,jluebbe/rauc,ejoerns/rauc,rauc/rauc,jluebbe/rauc,ejoerns/rauc,ejoerns/rauc,rauc/rauc,jluebbe/rauc