add installation instructions to pkg packages

pkg/unittest/lib/unittest.dart

 // Copyright (c) 2013, 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.
 
 /**
  * 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##
  *
  *  * __Tests__: Tests are specified via the top-level function [test], they can be
  *    organized together using [group].
  *  * __Checks__: Test expectations can be specified via [expect]
  *  * __Matchers__: [expect] assertions are written declaratively using the
  *    [Matcher] class.
  *  * __Configuration__: The framework can be adapted by calling [configure] with a
@@ skipping 122 matching lines @@
  *           guardAsync(() {
  *             int x = 2 + 3;
  *             expect(x, equals(5));
  *           });
  *           // indicate that the asynchronous callback was invoked.
  *           async.complete();
  *         });
  *       });
  *     }
  *
+ * [pub]: http://pub.dartlang.org
  */
 library unittest;
 
 import 'dart:async';
 import 'dart:isolate';
 import 'dart:collection';
 import 'matcher.dart';
 export 'matcher.dart';
 
 // TODO(amouravski): We should not need to import mock here, but it's necessary
@@ skipping 692 matching lines @@
 }
 
 /** Enable a test by ID. */
 void enableTest(int testId) => _setTestEnabledState(testId, true);
 
 /** Disable a test by ID. */
 void disableTest(int testId) => _setTestEnabledState(testId, false);
 
 /** Signature for a test function. */
 typedef dynamic TestFunction();