Aded docs on deserialization.

README.md

@@ -74,6 +74,7 @@ Or install it yourself as:
  * [Filtering and sorting](#filtering-and-sorting)
    * [Sorting using expressions](#sorting-using-expressions)
  * [Pagination](#pagination)
+ * [Deserialization](#deserialization)
 
 ---
 
@@ -303,8 +304,38 @@ use the `jsonapi_pagination_meta` method:
 
     { pagination: pagination } if pagination.present?
   end
+
+```
+### Deserialization
+
+`JSONAPI::Deserialization` provides a helper to transform a `JSONAPI` document
+into a flat dictionary that can be used to update an `ActiveRecord::Base` model.
+
+Here's an example using the `jsonapi_deserialize` helper:
+
+```ruby
+class MyController < ActionController::Base
+  include JSONAPI::Deserialization
+
+  def update
+    model = MyModel.find(params[:id])
+
+    if model.update(jsonapi_deserialize(only: [:attr1, :rel_one]))
+      render jsonapi: model
+    else
+      render jsonapi_errors: model.errors, status: :unprocessable_entity
+    end
+  end
+end
 ```
 
+The `jsonapi_deserialize` helper accepts the following options:
+
+ * `only`: returns exclusively attributes/relationship data in the provided list
+ * `except`: returns exclusively attributes/relationship which are not in the list
+ * `polymorphic`: will add and detect the `_type` attribute and class to the
+   defined list of polymorphic relationships
+
 ## Development
 
 After checking out the repo, run `bundle` to install dependencies.