[FIX] account: give a correct example

The computation was incorrect, the answer was 10, not 110 with the
previous formula

Courtesy of Frederico Freire Boaventura

closes odoo/odoo#44514

X-original-commit: 577e1ad8314cac6e61f60f997f338df4b7a1da38
Signed-off-by: Martin Trigaux (mat) <mat@odoo.com>