Update README.md

I found this problem when using InheritedResources. Here fix and explanation why rails/rails#9534

README.md

@@ -683,15 +683,15 @@ If you need `params.require` you can do it like this:
 
 ```ruby
 def permitted_params
-  {:widget => params.require(:widget).permit(:permitted_field, :other_permitted_field)}
+  {:widget => params.fetch(:widget, {}).permit(:permitted_field, :other_permitted_field)}
 end
 ```
 
 Or better yet just override `#build_resource_params` directly:
 
 ```ruby
 def build_resource_params
-  [params.require(:widget).permit(:permitted_field, :other_permitted_field)]
+  [params.fetch(:widget, {}).permit(:permitted_field, :other_permitted_field)]
 end
 ```