update README.md

Author: meowpunch

README.md

@@ -32,5 +32,7 @@
 ## Structural Patterns
 
 ## behavioral Patterns
+### [Visitor Pattern](https://en.wikipedia.org/wiki/Visitor_pattern)
+- the visitor design pattern is a way of separating an algorithm from an object structure on which it operates. A practical result of this separation is the ability to add new operations to existing object structures without modifying the structures. It is one way to follow the open/closed principle.
 
 ## Concurrency Patterns