Update README file

README.md

-## Google Cloud Platform
-
-High level interface for Google Cloud Platform APIs
+## Google Cloud Platform support package (gcloud)
+
+The `gcloud` package provides a high level "idomatic Dart" interface to
+some of the most widely used Google Cloud Platform services. Currently the
+following services are supported:
+
+  * Cloud Datastore
+  * Cloud Storage
+  * Cloud Pub/Sub
+
+The APIs in this package are all based on the generic generated APIs in the
+[googleapis] and [googleapis_beta][googleapisbeta] packages.
+
+This means that the authentication model for using the APIs in this package
+uses the [googleapis_auth][googleapisauth] package.
+
+Note that this package is only intended for being used with the standalone VM
+in a server or command line application. Don't expect this package to work on
+the browser.
+
+The code snippets below demonstrating the use of this package all assume that
+the following imports are present:
+
+```dart
+import 'package:googleapis_auth/auth_io.dart' as auth;
+import 'package:http/http.dart' as http;
+import 'package:gcloud/db.dart';
+import 'package:gcloud/storage.dart';
+import 'package:gcloud/pubsub.dart';
+import 'package:gcloud/service_scope.dart' as ss;
+import 'package:gcloud/src/datastore_impl.dart';
+```
+
+### Getting access to the APIs
+
+The first step in using the APIs is to get an authenticated HTTP client and
+with that create API class instances for accessing the different APIs. The
+code below assumes that you have a Google Cloud Project called `my-project`
+with credentials for a service account from that project stored in the file
+`my-project.json`.
+
+```dart
+// Read the service account credentials from the file.
+var jsonCredentials = new File('my-project.json').readAsStringSync();
+var credentials = new auth.ServiceAccountCredentials.fromJson(jsonCredentials);
+
+// Get an HTTP authenticated client using the service account credentials.
+var scopes = []
+    ..addAll(dastore_impl.DatastoreImpl.SCOPES);
+    ..addAll(Storage.SCOPES)
+    ..addAll(PubSub.SCOPES)
+var client = await auth.clientViaServiceAccount(creds, scopes);
+
+// Instantiate objects to access Cloud Datastore, Cloud Storage
+// and Cloud Pub/Sub APIs.
+var db = new DatastoreDB(
+    new dastore_impl.DatastoreImpl(client, 's~my-project'));
+var storage = new Storage(client, 'my-project');
+var pubsub = new PubSub(client, 'my-project');
+```
+
+All the APIs in this package supports the use of 'service scopes'. Service
+scopes are described in details below.
+
+```dart
+ss.fork(() {
+  // register the services in the new service scope.
+  registerDbService(db);
+  registerStorageService(storage);
+  registerPubSubService(pubsub);
+  
+  // Run application using these services.
+});
+```
+
+The services registered with the service scope can now be reached from within
+all the code running in the same service scope using the below getters.
+
+```dart
+dbService.
+storageService.
+pubsubService.
+```
+
+This way it is not necessary to pass the service objects around in your code.
+
+### Use with App Engine
+
+The `gcloud` package is also integrated in the Dart [appengine] package. This
+means the `gcloud` services are available both via the appengine context and
+service scopes. The authentication required to access the Google Cloud Platform
+services is handled automatically.
+
+This means that getting to the App Engine Datastore can be through either
+the App Engine context
+
+```dart
+var db = context.services.db;
+```
+
+or just using the service scope registration.
+
+```dart
+var db = dbService;
+```
+
+## Cloud Datastore
+Google Cloud Datastore provide a NoSQL, schemaless database for storing
+non-relational data. See the product page
+[https://cloud.google.com/datastore/][Datastore] for more information.
+
+The Cloud Datastore API provides a mapping of Dart objects to entities stored
+in the Datastore. The following example shows how to annotate a class to
+make it possible to store instances of it in the Datastore.
+
+```dart
+@db.Kind()
+class Person extends db.Model {
+  @db.StringProperty()
+  String name;
+
+  @db.IntProperty()
+  int age;
+}
+```
+
+The `Kind` annotation tell that instances of this class can be stored. The
+class must also inherit from `Model`. Now to store an object into the
+Datastore create an instance and use the `commit` function.
+
+```dart
+var person = new Person()
+    ..name = ''
+    ..age = 42;
+await db.commit(inserts: [person]);
+```
+
+The function `query` is used to build a `Query` object which can be run to
+perform the query.
+
+```dart
+var persons = (await db.query(Person).run()).toList();
+```
+
+NOTE: This package include a lower level API provided through the class
+`Datastore` on top of which the `DatastoreDB` API is build. The main reason
+for this additional API level is to bridge the gap between the different APIs
+exposed inside App Engine and through the public REST API. We reserve the
+rights to modify and maybe even remove this additional layer at any time.
+
+## Cloud Storage
+Google Cloud Storage provide a highly available object store (aka BLOB
+store). See the product page [https://cloud.google.com/storage/][GCS]
+for more information.
+
+In Cloud Storage the objects (BLOBs) are organized in _buckets_. Each bucket
+has a name in a global namespace. The following code creates a new bucket
+named `my-bucket` and writes the content of the file `my-file.txt` to the
+object named `my-object`.
+
+```dart
+var bucket = await storage.createBucket('my-bucket');
+new File('my-file.txt').openRead().pipe(bucket.write('my-object'));
+```
+
+The following code will read back the object.
+
+```dart
+bucket.read('my-object').pipe(new File('my-file-copy.txt').openWrite());
+```
+
+## Cloud Pub/Sub
+Google Cloud Pub/Sub provides many-to-many, asynchronous messaging. See the
+product page [https://cloud.google.com/pubsub/][PubSub] for more information.
+
+Cloud Pub/Sub uses two concepts for messaging. _Topics_ are used if you want
+to send messages and _subscriptions_ are used to subscribe to topics and
+receive the messages. This decouples the producer of a message from the
+consumer of a message.
+
+The following code creates a _topic_ and sends a simple test message:
+
+```dart
+var topic = await pubsub.createTopic('my'topic');
+await topic.publishString('Hello, world!')
+```
+
+With the following code a _subscription_ is created on the _topic_ and
+a message is pulled using the subscription. A received message must be
+acknowledged when the consumer has processed it. 
+
+```dart
+var subscription =
+    await pubsub.createSubscription('my-subscription', 'my-topic);
+var pullEvent = await subscription.pull();
+print(pullEvent.message.asString);
+await pullEvent.acknowledge()
+```
+
+It is also possible to receive messages using push events instead of pulling
+from the subscription. To do this the subscription should be configured as a
+push subscription with an HTTP endpoint.
+
+```dart
+await pubsub.createSubscription(
+    'my-subscription',
+    'my-topic',
+    endpoint: Uri.parse('https://server.example.com/push'));
+```
+
+With this subscription all messages will be send to the URL provided in the
+`endpoint` argument. The server needs to acknowledge the reception of the
+message with a `200 OK` reply.
 
 ### Running tests
 
 If you want to run the end-to-end tests, a Google Cloud project is required.
-When running these tests the following envrionment variables needs to be set:
+When running these tests the following environment variables need to be set:
 
     GCLOUD_E2E_TEST_PROJECT
     GCLOUD_E2E_TEST_KEY
 
 The vaule of the environment variable `GCLOUD_E2E_TEST_PROJECT` is the name
 of the Google Cloud project to use. The value of the environment variable
-`GCLOUD_E2E_TEST_KEY` is a Google Cloud Storage path (starting wiht `gs://`)
+`GCLOUD_E2E_TEST_KEY` is a Google Cloud Storage path (starting with `gs://`)
 to a JSON key file for a service account providing access to the Cloud Project. 
+
+[Datastore]: https://cloud.google.com/datastore/
+[GCS]: https://cloud.google.com/storage/
+[PubSub]: https://cloud.google.com/pubsub/
+[googleapis]: https://pub.dartlang.org/packages/googleapis
+[googleapisbeta]: https://pub.dartlang.org/packages/googleapis_beta
+[googleapisauth]: https://pub.dartlang.org/packages/googleapis_beta
+[appengine]: https://pub.dartlang.org/packages/appengine