Update README to point to new source location (#29)

diff --git a/README.md b/README.md
index 03c337f..5e63ada 100644
--- a/README.md
+++ b/README.md

@@ -1,24 +1 @@
-## Proxy for Shelf
-
-[![Build Status](https://github.com/dart-lang/shelf_proxy/workflows/Dart%20CI/badge.svg)](https://github.com/dart-lang/shelf_proxy/actions?query=workflow%3A"Dart+CI"+branch%3Amaster)
-
-`shelf_proxy` is a [Shelf][] handler that proxies requests to an external
-server. It can be served directly and used as a proxy server, or it can be
-mounted within a larger application to proxy only certain URLs.
-
-[Shelf]: https://pub.dev/packages/shelf
-
-```dart
-import 'package:shelf/shelf_io.dart' as shelf_io;
-import 'package:shelf_proxy/shelf_proxy.dart';
-
-void main() async {
-  var server = await shelf_io.serve(
-    proxyHandler("https://dart.dev"),
-    'localhost',
-    8080,
-  );
-
-  print('Proxying at http://${server.address.host}:${server.port}');
-}
-```
+This package has moved to https://github.com/dart-lang/shelf/tree/master/pkgs/shelf_proxy