Add documentation

README.markdown

@@ -602,6 +602,51 @@ knp_gaufrette:
                 container_name: foo
 ```
 
+## GoogleCloudStorage
+
+Adapter for Google APIs Client Library for PHP.
+
+### Parameters
+
+ * `service_id` The service id of the `\Google_Service_Storage` to use. *(required)*
+ * `bucket_name` The name of the GCS bucket to use. *(required)*
+ * `detect_content_type`: if `true` will detect the content type for each file *(default `true`)*
+ * `options` A list of additional options passed to the adapter.
+   * `directory` A directory to operate in. *(default '')*
+   * `acl` Whether the uploaded files should be `private` or `public` *(default `private`)*
+
+### Defining services
+
+You need to create a custom factory service which creates a `\Google_Client` and authorizes with the correct scopes 
+and then returns a `\Google_Service_Storage` class connected to the client class:
+
+```yaml
+services:
+    app.google_cloud_storage.service:
+        class: \Google_Service_Storage
+        factory_class: App\Factory\GoogleCloudStorageServiceFactory
+        factory_method: 'createService'
+        arguments:
+            -
+                # all the arguments needed like service account email and path to key.p12
+```
+
+### Example
+
+Once the service is set up use its key as the `service_id` in the gaufrette configuration:
+
+``` yaml
+# app/config/config.yml
+knp_gaufrette:
+    adapters:
+        profile_photos:
+            google_cloud_storage:
+                service_id: 'app.google_cloud_storage.service'
+                bucket_name: 'images'
+                options:
+                    directory: 'profile_photos'
+```
+
 ## Cache (cache)
 
 Adapter which allows you to cache other adapters