Document default LogLevel (dart-archive#58)

README.md

@@ -10,7 +10,7 @@ messages.
 Here is a simple logging configuration that logs all messages via `print`.
 
 ```dart
-Logger.root.level = Level.ALL;
+Logger.root.level = Level.ALL; // defaults to Level.INFO
 Logger.root.onRecord.listen((record) {
   print('${record.level.name}: ${record.time}: ${record.message}');
 });