docs: diagrams for unit of work, update method, and value object

value-object/README.md

@@ -43,6 +43,10 @@ Wikipedia says
 
 > In computer science, a value object is a small object that represents a simple entity whose equality is not based on identity: i.e. two value objects are equal when they have the same value, not necessarily being the same object.
 
+Flowchart
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+![Value Object Pattern Flowchart](./etc/value-object-flowchart.png)
+
 ## Programmatic Example of Value Object Pattern in Java
 
 There is a class for hero statistics in a role-playing game. The statistics contain attributes such as strength, intelligence, and luck. The statistics of different heroes should be equal when all the attributes are equal.