Added some comments about immutability Commands

Author: CESARDELATORRE

src/Services/Ordering/Ordering.API/Application/Commands/CreateOrderCommand.cs

@@ -5,6 +5,15 @@
 
 namespace Microsoft.eShopOnContainers.Services.Ordering.API.Application.Commands
 {
+    // DDD and CQRS patterns comment: Note that it is recommened to implement immutable Commands
+    // In this case, its immutability is achieved by having all the setters as private
+    // plus only being able to update the data just once, when creating the object through its constructor.
+    // References on Immutable Commands:  
+    // http://cqrs.nu/Faq
+    // https://docs.spine3.org/motivation/immutability.html 
+    // http://blog.gauffin.org/2012/06/griffin-container-introducing-command-support/
+    // https://msdn.microsoft.com/en-us/library/bb383979.aspx
+
     [DataContract]
     public class CreateOrderCommand
         :IAsyncRequest<bool>