add image flutter code example

Example 1: flutter image asset

// pubspec.yaml
flutter:
  assets:
    - graphics/

// Inside your widget
Image(image: AssetImage('graphics/background.png'))

Example 2: flutter asset image not showing

flutter:  
  uses-material-design: true   
  assets:   
    - assets/

class _UserLoginState extends State<UserLogin> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stack(
        children: <Widget>[
          Image(image: AssetImage("assets/christmas.jpeg"),
          fit: BoxFit.cover,
        ],
      )
    );
  }
}

Example 3: image in flutter

const Image(
  image: NetworkImage('https://flutter.github.io/assets-for-api-docs/assets/widgets/owl.jpg'),
)