Added strategy to Readme index

Author: frnlpz

README.md

@@ -14,9 +14,10 @@ Kotlin OOP and FP Design Patterns
     * [ ] [Mediator](#mediator)
     * [ ] [Memento](#memento)
     * [ ] [Null Object](#null-object)
-    * [x] [Observer](#observer)
-    * [x] [State](#state)
-    * [ ] [Template](#template)
+    * [x] [Observer](#observer)
+    * [x] [State](#state)
+    * [x] [Strategy](#strategy)
+    * [ ] [Template](#template)
     * [ ] [Visitor](#visitor)
   * [Creational Patterns](#creational)
     * [ ] [Abstract Factory](#abstract-factory)