Update docs for #212

Author: markstory

docs/Quick-start-and-introduction.md

@@ -20,13 +20,25 @@ Example of configuring the authentication middleware using `authentication` appl
 
 ```php
 use Authentication\AuthenticationService;
-use Authentication\AuthenticationServiceInterface;
+use Authentication\AuthenticationServiceProviderInterface;
 use Authentication\Middleware\AuthenticationMiddleware;
+use Psr\Http\Message\ResponseInterface;
+use Psr\Http\Message\ServerRequestInterface;
 
-class Application extends BaseApplication
+class Application extends BaseApplication implements AuthenticationServiceProviderInterface
 {
-    public function authentication(AuthenticationServiceInterface $service)
+
+    /**
+     * Returns a service provider instance.
+     *
+     * @param \Psr\Http\Message\ServerRequestInterface $request Request
+     * @param \Psr\Http\Message\ResponseInterface $response Response
+     * @return \Authentication\AuthenticationServiceInterface
+     */
+    public function getAuthenticationService(ServerRequestInterface $request, ResponseInterface $response)
     {
+        $service = new AuthenticationService();
+
         $fields = [
             'username' => 'email',
             'password' => 'password'