docs: add mvvm architecture diagram

Author: iluwatar

Diff for: model-view-viewmodel/README.md

@@ -42,6 +42,11 @@ Wikipedia says
 
 > Model–view–viewmodel (MVVM) is a software architectural pattern that facilitates the separation of the development of the graphical user interface (the view) – be it via a markup language or GUI code – from the development of the business logic or back-end logic (the model) so that the view is not dependent on any specific model platform. 
 
+Architecture diagram
+
+![Model-View-ViewModel Architecture Diagram](./etc/mvvm-architecture-diagram.png)
+
+
 ## Programmatic Example of Model-View-ViewModel Pattern in Java
 
 ViewModel will hold the business logic and expose the data from model to View.