minor #12065 SwiftMailer Section - Added more information (TheGarious)

This PR was merged into the 4.3 branch.

Discussion
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SwiftMailer Section - Added more information

Add comment for template location.

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Commits
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f4db2c5 SwiftMailer Section - Added more information

Author: javiereguiluz

email.rst

@@ -82,6 +82,7 @@ sending an email is pretty straightforward::
             // you can remove the following code if you don't define a text version for your emails
             ->addPart(
                 $this->renderView(
+                    // templates/emails/registration.txt.twig
                     'emails/registration.txt.twig',
                     ['name' => $name]
                 ),