add installation instructions to pkg packages

pkg/logging/lib/logging.dart

 // Copyright (c) 2012, 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.
 
 /**
  * Provides APIs for debugging and error logging. This library introduces
  * abstractions similar to those used in other languages, such as the Closure JS
  * Logger and java.util.logging.Logger.
+ *
+ * ## Installing ##
+ *
+ * Use [pub][] to install this package. Add the following to your `pubspec.yaml`
+ * file.
+ *
+ *     dependencies:
+ *       logging: any
+ *
+ * And then run `pub install`.
+ *
+ * [pub]: http://pub.dartlang.org
  */
 library logging;
 
 import 'dart:async';
 
 /**
  * Whether to allow fine-grain logging and configuration of loggers in a
  * hierarchy. When false, all logging is merged in the root logger.
  */
 bool hierarchicalLoggingEnabled = false;
@@ skipping 277 matching lines @@
 
   /** Associated exception message (if any) when recording errors messages. */
   String exceptionText;
 
   LogRecord(
       this.level, this.message, this.loggerName,
       [time, this.exception, this.exceptionText]) :
     this.time = (time == null) ? new DateTime.now() : time,
     this.sequenceNumber = LogRecord._nextNumber++;
 }