Mark the package discontinued in the readme (#24)

diff --git a/README.md b/README.md
index e86dbe6..bc1c76b 100644
--- a/README.md
+++ b/README.md

@@ -1,29 +1,4 @@
-Middleware for the [`http`](https://pub.dev/packages/http) package that
-transparently retries failing requests.
+This package has been discontinued. You can find the functionality in
+[`package:http/retry.dart`][retry_library]
 
-To use this, just create an [`RetryClient`][RetryClient] that wraps the
-underlying [`http.Client`][Client]:
-
-[RetryClient]: https://pub.dev/documentation/http_retry/latest/http_retry/RetryClient-class.html
-[Client]: https://pub.dev/documentation/http/latest/http/Client-class.html
-
-```dart
-import 'package:http/http.dart' as http;
-import 'package:http_retry/http_retry.dart';
-
-Future<void> main() async {
-  final client = RetryClient(http.Client());
-  try {
-    print(await client.read('http://example.org'));
-  } finally {
-    client.close();
-  }
-}
-```
-
-By default, this retries any request whose response has status code 503
-Temporary Failure up to three retries. It waits 500ms before the first retry,
-and increases the delay by 1.5x each time. All of this can be customized using
-the [`RetryClient()`][new RetryClient] constructor.
-
-[new RetryClient]: https://pub.dev/documentation/http_retry/latest/http_retry/RetryClient/RetryClient.html
+[retry_library]: https://pub.dev/documentation/http/latest/retry/retry-library.html