Update README.md

Author: vandadnp

README.md

@@ -1,5 +1,6 @@
 # Table of Contents
 
+* [Map with Index in Dart](#map-with-index-in-dart)
 * [`Set` Comprehension in Dart](#set-comprehension-in-dart)
 * [Stretching `GridView` Items in Flutter](#stretching-gridview-items-in-flutter)
 * [Email Drag and Drop in Flutter](#email-drag-and-drop-in-flutter)
@@ -319,6 +320,12 @@
 * [Extract Minimum and Maximum Values in `List<num>` in Dart](#4-lines-of-dart-code-that-include-the-spread-operator-cascade-operator-generics-extensions-private-prefix-and-getters)
 * [Functions as First Class Citizens in Dart](#functions-as-first-class-citizens-in-dart)
 
+# Map with Index in Dart
+
+[Source Code](source/map-with-index-in-dart.dart)
+
+![](images/map-with-index-in-dart.jpg)
+
 # `Set` Comprehension in Dart
 
 [Source Code](source/set-comprehension-in-dart.dart)