extra detail for the OnDemandPercentage param description

Author: yob

templates/aws-stack.yml

@@ -223,7 +223,7 @@ Parameters:
     Default: 0
 
   OnDemandPercentage:
-    Description: Percentage of total instances that should launch as OnDemand. Default is 100% OnDemand - reduce this to use some Spot Instances when they're available and cheaper than the OnDemand price.
+    Description: Percentage of total instances that should launch as OnDemand. Default is 100% OnDemand - reduce this to use some Spot Instances when they're available and cheaper than the OnDemand price. A value of 70 means 70% OnDemand and 30% Spot Instances.
     Type: Number
     Default: 100
     MinValue: 0