Add note to response docs about the need to define the response_template...

Should help with #29 and #9.
I would move the explanation right after the teapot example, and would expand on it a bit more.

How about something more descriptive like:

*Note:* Remember that each of the response classes you create in the runtime part of your application, will need a corresponding response definition part in the design area that shares the same name. So make sure you register a corresponding template using the `register_response` DSL that the ApiDefinition class provides. In this case, we would need to register a template named `:tea_pot`, which must match a status code of 418 and a 'X-TeaPot' header of value 'MadeInJapan'. See [Response Definitions](../response-definitions/) for more information on how to do that. If you don't register a template for each of your classes, you will not be able to refer to them in your `response` stanzas of your actions in your ResourceDefinitions.