Add explicit total cost formula to documentation?

[anthonysantella]

I don't think there is any real ambiguity, but I think having an explicit cost formula for what is minimized in documentation would be reassuring when trying to debug weight tuning and understand what role different set sizes has in weight parameter influence. e.g.
final cost to minimize=sum over costs types: c (weight_c*(sum over items in relevant set for c: i(constant_c+cost_c_i))) (hopefully that's right!)