Autofill URL and TOKEN in debug mode. (#123)

* Autofill URL and TOKEN in debug mode.

* dart format.

* Set ENV priority higher than prefs.

example/README.md

@@ -1,3 +1,14 @@
 # LiveKit Flutter Example
 
 This app implements a video room using LiveKit's Flutter SDK. Designed to run for iOS, Android, and web.
+
+## Quickstart
+
+Run example:
+
+```bash
+flutter pub get
+# Due to the inconvenience of typing on mobile devices, 
+# you can autofill URL and TOKEN for first run in debug mode.
+flutter run --dart-define=URL=ws://${LIVEKIT_SERVER_IP}:7880 --dart-define=TOKEN=${YOUR_TOKEN}
+```

example/lib/pages/connect.dart

@@ -48,8 +48,12 @@ class _ConnectPageState extends State<ConnectPage> {
   // Read saved URL and Token
   Future<void> _readPrefs() async {
     final prefs = await SharedPreferences.getInstance();
-    _uriCtrl.text = prefs.getString(_storeKeyUri) ?? '';
-    _tokenCtrl.text = prefs.getString(_storeKeyToken) ?? '';
+
+    _uriCtrl.text = String.fromEnvironment('URL',
+        defaultValue: prefs.getString(_storeKeyUri) ?? '');
+    _tokenCtrl.text = String.fromEnvironment('TOKEN',
+        defaultValue: prefs.getString(_storeKeyToken) ?? '');
+
     setState(() {
       _simulcast = prefs.getBool(_storeKeySimulcast) ?? true;
       _adaptiveStream = prefs.getBool(_storeKeyAdaptiveStream) ?? true;