Changed calculation from Base Cost per Income to Return on Investment (Issue #3 (partly), #28, #52) with the formula from @svschouw and minor README edit

src/Sim.js

@@ -357,6 +357,9 @@ CM.Sim.BuyBuildings = function(amount, target) {
 		
 		CM.Cache[target][i] = {};
 		CM.Cache[target][i].bonus = CM.Sim.cookiesPs - Game.cookiesPs;
+		if (amount != 1) {
+			CM.Cache[target][i].price = CM.Sim.BuildingGetPrice(Game.Objects[i].basePrice, Game.Objects[i].amount, Game.Objects[i].free, amount);
+		}
 	}
 }