como poner border radius a image.asset

import 'package:flutter/material.dart';

class AvatarPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Avatar Page'),
        actions: <Widget>[
          Container(
            padding: EdgeInsets.all(5.0),
            child: CircleAvatar(
              backgroundImage: NetworkImage('https://www.salud180.com/sites/default/files/styles/encabezado_articulo/public/imagenes/2018/10/que-es-el-yoga.jpg?itok=XcNdWKs4'),
              radius: 25.0,
            ),
          ),
          Container(
            margin: EdgeInsets.only(right: 10.0),
            child: CircleAvatar(
              child: Text('SL'),
              backgroundColor: Colors.brown,
            ),
          )
        ],
      ),
      body: Center(
        child: FadeIn