add installation instructions to pkg packages

pkg/unittest/lib/unittest.dart

Index: pkg/unittest/lib/unittest.dart
diff --git a/pkg/unittest/lib/unittest.dart b/pkg/unittest/lib/unittest.dart
index 50d308b8d26c0d27b8b81441d1db82c5b0f4b929..96328aceee31f79932378baf994979ad62350aff 100644
--- a/pkg/unittest/lib/unittest.dart
+++ b/pkg/unittest/lib/unittest.dart
@@ -5,9 +5,17 @@
 /**
  * A library for writing dart unit tests.
  *
- * To import this library, install the
- * [unittest package](http://pub.dartlang.org/packages/unittest) via the pub
- * package manager. See the [Getting Started](http://pub.dartlang.org/doc)
+ * ## Installing ##
+ *
+ * Use [pub][] to install this package. Add the following to your `pubspec.yaml`

[Andrei Mouravski, 2013/04/19 20:13:35]

Actually, it might be good to say "the pub package manager" instead of just
"pub".

[sethladd, 2013/04/19 20:32:43]

I added clarification for every file.

+ * file.
+ *
+ *     dependencies:
+ *       unittest: any
+ *
+ * And then run `pub install`.
+ *
+ * See the [Getting Started](http://pub.dartlang.org/doc)
  * guide for more details.
  *
  * ##Concepts##
@@ -150,6 +158,7 @@
  *       });
  *     }
  *
+ * [pub]: http://pub.dartlang.org
  */
 library unittest;