add installation instructions to pkg packages

pkg/unittest/lib/mock.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.
 
 /**
  * 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 {};
  *
  * Then specify the [Behavior] of the Mock for different methods using
  * [when] (to select the method and parameters) and then the [Action]s
  * for the [Behavior] by calling [thenReturn], [alwaysReturn], [thenThrow],
  * [alwaysThrow], [thenCall] or [alwaysCall].
  *
  * [thenReturn], [thenThrow] and [thenCall] are one-shot so you would
@@ skipping 62 matching lines @@
  *     }
  *
  *     class MockFoo extends Mock implements Foo {
  *       Foo real;
  *       MockFoo() {
  *         real = new Foo();
  *         this.when(callsTo('bar')).alwaysCall(real.bar);
  *       }
  *     }
  *
+ * [pub]: http://pub.dartlang.org
  */
 
 library mock;
 
 import 'dart:mirrors' show MirrorSystem;
 
 import 'matcher.dart';
 
 /**
  * The error formatter for mocking is a bit different from the default one
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       }
     }
   }
 
   /** Clear both logs and behavior. */
   void reset() {
     resetBehavior();
     clearLogs();
   }
 }