add atom example

example/main.dart

@@ -1,8 +1,11 @@
 import 'package:http/http.dart' as http;
+import 'package:webfeed/domain/atom_feed.dart';
 import 'package:webfeed/domain/rss_feed.dart';
 
 void main() {
   var client = new http.Client();
+
+  // RSS feed
   client.get("https://developer.apple.com/news/releases/rss/releases.rss").then((response) {
     return response.body;
   }).then((bodyString) {
@@ -10,4 +13,13 @@ void main() {
     print(channel);
     return channel;
   });
+
+  // Atom feed
+  client.get("https://www.theverge.com/rss/index.xml").then((response) {
+    return response.body;
+  }).then((bodyString) {
+    var feed = new AtomFeed.parse(bodyString);
+    print(feed);
+    return feed;
+  });
 }