Document the unit of values in different sheets in the results file.

Recently, there was some confusion in the units of values in different sheets in the results file. For example, the unit of values in `cost_discounted_total` is million CUR, however, the unit of values in other cost sheets is just CUR. It'd be good to document the units somewhere - perhaps in the tutorial as including the unit in the results file might interfere with the current code structure.