Recipe for a New Page is missing some critical code for working correctly (19.01)

[fjsteves]

In viewing https://github.com/userfrosting/learn/blob/master/pages/19.recipes/01.creating-a-new-page/docs.md, there was an issue getting a new page to work properly. Adding the following use statements to the top corrected it:

use Psr\Http\Message\ResponseInterface as Response;

use Psr\Http\Message\ServerRequestInterface as Request;