food.modifier.formula: Clarify expected output of formula

[rikpronk]

The configuration gives no hint as to what the internal use of the option is. This leaves ambiguity regarding what users should strive to output, such as a percentage, absolute substraction, entire saturation value, or something else.

Currently this must be inferred by sampling different inputs or searching across forums and issues to find hints.

[ghost]

Perhaps a way to easily affect the default formula? I just wanted to nerf it a little. Slow down the loss and raise the minimum so it wouldn't stop you from living on baked potatoes, just make it less effective.