Increase package description to >=60 characters and added an example (#41)

Follow conventions, improve package score
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 011af57..760802e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,4 @@
-## 3.0.0-nullsafety
+## 3.0.0-nullsafety.0
 
 Pre-release for the null safety migration of this package.
 
diff --git a/example/example.dart b/example/example.dart
new file mode 100644
index 0000000..5038591
--- /dev/null
+++ b/example/example.dart
@@ -0,0 +1,20 @@
+// 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 'dart:convert';
+
+import 'package:convert/convert.dart';
+
+void main(List<String> args) {
+  // Creates a Codec that converts a UTF-8 strings to/from percent encoding
+  final fusedCodec = utf8.fuse(percent);
+
+  final input = args.isNotEmpty ? args.first : 'ABC 123 @!(';
+  print(input);
+  final encodedMessage = fusedCodec.encode(input);
+  print(encodedMessage);
+
+  final decodedMessage = fusedCodec.decode(encodedMessage);
+  assert(decodedMessage == input);
+}
diff --git a/pubspec.yaml b/pubspec.yaml
index d3cdea4..b41eb15 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,6 +1,8 @@
 name: convert
-version: 3.0.0-nullsafety
-description: Utilities for converting between data representations.
+version: 3.0.0-nullsafety.0
+description: >-
+  Utilities for converting between data representations.
+  Provides a number of Sink, Codec, Decoder, and Encoder types.
 repository: https://github.com/dart-lang/convert
 
 environment: