Fix asset methods and remove comment

Author: kevinvennitti

content/docs/1_guide/16_emails/guide.txt

@@ -277,9 +277,8 @@ $kirby->email([
     // …
 		'template' => 'email',
     'beforeSend' => function ($mailer) {
-				// $image should return file path
-				$image = asset('assets/images/logo.png')->root();
-        $mailer->AddEmbeddedImage($image, 'image', $image->filename(), 'base64', $image->mime());
+				$image = asset('assets/images/logo.png');
+				$mailer->AddEmbeddedImage($image->root(), 'image', $image->filename(), 'base64', $image->mime());
 
         return $mailer;
     }