Update url_launcher README (#4)

Author: szakarias

packages/url-launcher/README.md

@@ -1,7 +1,45 @@
 # url_launcher
 
-A Flutter plugin for launching a URL.
+A Flutter plugin for launching a URL in the mobile platform. Supports iOS and Android.
 
-## Getting Started
+## Usage
+To use this plugin, add url_launcher as a [dependency in your pubspec.yaml file](https://flutter.io/platform-plugins/).
+
+### Example
+
+``` dart
+import 'package:flutter/material.dart';
+import 'package:url_launcher/url_launcher.dart';
+
+void main() {
+  runApp(new Scaffold(
+    body: new Center(
+      child: new RaisedButton(
+        onPressed: launchURL,
+        child: new Text('Show Flutter homepage'),
+      ),
+    ),
+  ));
+}
+
+launchURL() {
+  UrlLauncher.launch('https://flutter.io');
+}
+
+```
+
+## Supported URL schemes
+
+The `launch` method takes a string argument containing a URL. This URL
+can be formatted using a number of different URL schemes. The supported
+URL schemes depend on the underlying platform and installed apps.
+
+Common schemes supported by both iOS and Android:
+
+* http:<URL> , https:<URL>
+* mailto:<email-address>
+* tel:<phone-number>
+* sms:<phone-number>
+
+More details can be found here for [iOS](https://developer.apple.com/library/content/featuredarticles/iPhoneURLScheme_Reference/Introduction/Introduction.html) and [Android](https://developer.android.com/guide/components/intents-common.html)
 
-Try out the plugin by running the project in the example/ folder.