add installation instructions to pkg packages

pkg/unittest/lib/mock.dart

Index: pkg/unittest/lib/mock.dart
diff --git a/pkg/unittest/lib/mock.dart b/pkg/unittest/lib/mock.dart
index 9ee6d8a80ce0479a40c6fc4258538304a9822e53..1f215d84be7c5b973d00559b9a81b248b34d7580 100644
--- a/pkg/unittest/lib/mock.dart
+++ b/pkg/unittest/lib/mock.dart
@@ -5,6 +5,18 @@
 /**
  * A simple mocking/spy library.
  *
+ * ## Installing ##
+ *
+ * Use [pub][] to install this package. Add the following to your `pubspec.yaml`
+ * file.
+ *
+ *     dependencies:
+ *       mock: any
+ *
+ * And then run `pub install`.
+ *
+ * ## Using ##
+ *
  * To create a mock objects for some class T, create a new class using:
  *
  *     class MockT extends Mock implements T {};
@@ -87,6 +99,7 @@
  *       }
  *     }
  *
+ * [pub]: http://pub.dartlang.org
  */
 
 library mock;