Adjust chapter "Supplements" to remove ChargeTypeCode 12 in calculation description

In #74 (closed) the group decided to deprecate ChargeType 12 and replace with 24. This will simplify the documentation but is a (small) breaking change.

The paragraph has been updated with merge request !92 (diffs)

In any case the calculation description still talks about ChargeTypeCode 12 in file 045-rateplan.adoc on line 448

@xlbitTech Do you confirm?