add scrollable flutter code example

Example 1: make scaffold scrollable flutter

@override
 Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(
      title: Text('News'),
    ),
    body: SingleChildScrollView(  // <-- wrap this around
      child: Column(
        children: [
        ],
      ),
    ));
  }

Example 2: viewportConstraints

Widget build(BuildContext context) {
  return LayoutBuilder(
    builder: (BuildContext context, BoxConstraints viewportConstraints) {
      return SingleChildScrollView(
        child: ConstrainedBox(
          constraints: BoxConstraints(
            minHeight: viewportConstraints.maxHeight,
          ),
          child: Column(
            mainAxisSize: MainAxisSize.min,
            mainAxisAlignment: MainAxisAlignment.spaceAround,
            children: [
              Container(
                // A fixed-height child.
                color: const Color(0xff808000), // Yellow
                height: 120.0,
              ),
              Container(
                // Another fixed-height child.
                color: const Color(0xff008000), // Green
                height: 600.0,
              ),
            ],
          ),
        ),
      );
    },
  );
}