add installation instructions to pkg packages

pkg/logging/lib/logging.dart

Index: pkg/logging/lib/logging.dart
diff --git a/pkg/logging/lib/logging.dart b/pkg/logging/lib/logging.dart
index 222ff1e426b67e03bc149dc934fecc660834543a..d3888def864b439754ddae8ccea299c357eb758d 100644
--- a/pkg/logging/lib/logging.dart
+++ b/pkg/logging/lib/logging.dart
@@ -6,6 +6,18 @@
  * 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;