Update integration_test README (flutter#3824)

* Change deprecated to moved

- add a link to the flutter.dev docs
- add a link to the new location 
- Changed "deprecated" to "moved" to avoid confusion,
  since this is still the recommended way to write unit tests,
  but needs to be imported differently.

* Update packages/integration_test/README.md

* Apply suggestions from code review

Co-authored-by: Shams Zakhour (ignore Sfshaza) <[email protected]>

Co-authored-by: Shams Zakhour (ignore Sfshaza) <[email protected]>

packages/integration_test/README.md

@@ -1,16 +1,22 @@
-# integration_test (deprecated)
+# integration_test (moved)
 
-## DEPRECATED
+## MOVED
 
-This package has been moved to the Flutter SDK. Starting with Flutter 2.0,
-it should be included as:
+This package has [moved to the Flutter
+SDK](https://github.com/flutter/flutter/tree/master/packages/integration_test),
+and the pub.dev version is deprecated.
+As of Flutter 2.0, include it in your pubspec's
+dev dependencies section, as follows:
 
 ```
 dev_dependencies:
   integration_test:
     sdk: flutter
 ```
 
+For the latest documentation, see [Integration
+testing](https://flutter.dev/docs/testing/integration-tests).
+
 ## Old instructions
 
 This package enables self-driving testing of Flutter code on devices and emulators.