Added covid-19 example app and Updated the readme (#73)

covid19_mobile_app/lib/main.dart

@@ -0,0 +1,19 @@
+import 'package:flutter/material.dart';
+import 'screens/home.dart';
+
+void main() => runApp(MyApp());
+
+class MyApp extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      title: 'Covid-19',
+      theme: ThemeData(
+        primarySwatch: Colors.blue,
+        accentColor: Color(0xfff4796b),
+        brightness: Brightness.dark,
+      ),
+      home: Home(),
+    );
+  }
+}