Add ChangeNotifier and ValueNotifier tutorials (#3997)

Co-authored-by: Kamran Ahmed <kamranahmed.se@gmail.com>

src/data/roadmaps/flutter/content/111-state-management/106-value-notifier.md

@@ -1,4 +1,8 @@
 # Value Notifier
 
-- [ValueNotifier class - Flutter](https://api.flutter.dev/flutter/foundation/valuenotifier-class.html)
+Flutter's ValueNotifier is a lightweight tool for state management in Flutter. It efficiently handles a single value and notifies listeners of changes. With ValueNotifier, developers can easily track and update specific data, such as counters or user inputs. It simplifies state management and enables dynamic Flutter interfaces.
+
+Visit the following resources to learn more:
+
+- [ValueNotifier class - Flutter](https://api.flutter.dev/flutter/foundation/ValueNotifier-class.html)
 - [ValuerNotifier & ValueListenableBuilder](https://medium.com/@avnishnishad/flutter-communication-between-widgets-using-valuenotifier-and-valuelistenablebuilder-b51ef627a58b)

src/data/roadmaps/flutter/content/111-state-management/107-change-notifier.md

@@ -1,4 +1,8 @@
 # Change Notifier
 
-- [ChangeNotifier class - Flutter](https://api.flutter.dev/flutter/foundation/changenotifier-class.html)
+Flutter's ChangeNotifier is a fundamental class for state management in Flutter. It allows developers to handle and notify listeners of data changes, ensuring efficient updates to the user interface. By extending ChangeNotifier, developers can create custom classes to represent specific states or data models. Integrating ChangeNotifier enhances the user experience by managing state and dynamically updating the UI. It simplifies state management and enables the creation of interactive Flutter applications.
+
+Visit the following resources to learn more:
+
+- [ChangeNotifier class - Flutter](https://api.flutter.dev/flutter/foundation/ChangeNotifier-class.html)
 - [Simple app state management](https://docs.flutter.dev/data-and-backend/state-mgmt/simple)