Update outside_controller_use.md (#2047)

* Update outside_controller_use.md

Provide example for options parameter when serializing a resource.

Author: NickOttrando

docs/howto/outside_controller_use.md

@@ -10,8 +10,8 @@ In ActiveModelSerializers versions 0.10 or later, serializing resources outside
 # Create our resource
 post = Post.create(title: "Sample post", body: "I love Active Model Serializers!")
 
-# Optional options parameters
-options = {}
+# Optional options parameters for both the serializer and instance
+options = {serializer: PostDetailedSerializer, username: 'sample user'}
 
 # Create a serializable resource instance
 serializable_resource = ActiveModelSerializers::SerializableResource.new(post, options)
@@ -20,6 +20,7 @@ serializable_resource = ActiveModelSerializers::SerializableResource.new(post, o
 model_json = serializable_resource.as_json
 ```
 The object that is passed to `ActiveModelSerializers::SerializableResource.new` can be a single resource or a collection.
+The additional options are the same options that are passed [through controllers](../general/rendering.md#explicit-serializer).
 
 ### Looking up the Serializer for a Resource