Added outline for behavioral design patterns.

README.md

@@ -151,4 +151,69 @@ TODO
 
 ## Behavioral Design Patterns
 
+In plain words:
+
+> It is concerned with assignment of responsibilities between the objects. What
+makes them different from structural patterns is they don't just specify the
+structure but also outline the patterns for message passing/communication
+between them. Or in other words, they assist in answering "How to run a behavior
+in software component?"
+
+Wikipedia says:
+
+> In software engineering, behavioral design patterns are design patterns that
+identify common communication patterns between objects and realize these
+patterns. By doing so, these patterns increase flexibility in carrying out this
+communication.
+
+* [Chain of Responsibility](#-chain-of-responsibility)
+* [Command](#-command)
+* [Iterator](#-iterator)
+* [Mediator](#-mediator)
+* [Memento](#-memento)
+* [Observer](#-observer)
+* [Visitor](#-visitor)
+* [Strategy](#-strategy)
+* [State](#-state)
+* [Template Method](#-template-method)
+
+### 🔗 Chain of Responsibility
+
 TODO
+
+### 👮 Command
+
+TODO
+
+### ➿ Iterator
+
+TODO
+
+### 👽 Mediator
+
+TODO
+
+### 💾 Memento
+
+TODO
+
+### 😎 Observer
+
+TODO
+
+### 🏃 Visitor
+
+TODO
+
+### 💡 Strategy
+
+TODO
+
+### 💢 State
+
+TODO
+
+### 📒 Template Method
+
+TODO
+