fix(docs): corrected vector from rear axis to sensor mounting point (#456)

* fix(docs): corrected vector from rear axis to sensor mounting point and separated virtual mounting position from middle of rear axle

Signed-off-by: Katrin Mehl <katrin.mehl@parson-europe.com>
Co-authored-by: Stefan Cyliax <stefan.cyliax@asam.net>

Author: paagkame