Add an example

example/example.dart

diff --git a/example/example.dart b/example/example.dart
new file mode 100644
index 0000000..9230b6a
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+++ b/example/example.dart
@@ -0,0 +1,16 @@
+// Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import 'package:http_parser/http_parser.dart';
+
+void main() {
+  final date = DateTime.utc(2014, 9, 9, 9, 9, 9);
+  print(date); // 2014-09-09 09:09:09.000Z
+
+  final httpDateFormatted = formatHttpDate(date);
+  print(httpDateFormatted); // Tue, 09 Sep 2014 09:09:09 GMT
+
+  final nowParsed = parseHttpDate(httpDateFormatted);
+  print(nowParsed); // 2014-09-09 09:09:09.000Z
+}

test/example_test.dart

diff --git a/test/example_test.dart b/test/example_test.dart
new file mode 100644
index 0000000..ef61060
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+++ b/test/example_test.dart
@@ -0,0 +1,19 @@
+import 'dart:io';
+
+import 'package:test/test.dart';
+
+void main() {
+  test('validate example', () {
+    final result = Process.runSync(
+      Platform.executable,
+      ['example/example.dart'],
+    );
+
+    expect(result.exitCode, 0);
+    expect(result.stdout, '''
+2014-09-09 09:09:09.000Z
+Tue, 09 Sep 2014 09:09:09 GMT
+2014-09-09 09:09:09.000Z
+''');
+  }, testOn: 'vm');
+}