feature #4941 Adding a section to emailing showing off absolute_url (weaverryan)

This PR was merged into the 2.7 branch.

Discussion
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Adding a section to emailing showing off absolute_url

Hi guys!

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | no (but follows from symfony/symfony#13264)
| Applies to    | 2.7+
| Fixed tickets | n/a

I thought we should show off `absolute_url` in a place where you will commonly need it.

Thanks!

Commits
-------

67efb2b minor tweak thanks to Javier
5ab1adf Adding a section to emailing showing off absolute_url

Author: weaverryan

cookbook/email/email.rst

@@ -123,7 +123,21 @@ an email is pretty straightforward::
     }
 
 To keep things decoupled, the email body has been stored in a template and
-rendered with the ``renderView()`` method.
+rendered with the ``renderView()`` method. The ``registration.html.twig``
+template might look something like this:
+
+.. code-block:: html+jinja
+
+    {# app/Resources/views/Emails/registration.html.twig #}
+    <h3>You did it! You registered!</h3>
+
+    {# example, assuming you have a route named "login" $}
+    To login, go to: <a href="{{ url('login') }}">...</a>.
+
+    Thanks!
+
+    {# Makes an absolute URL to the /images/logo.png file #}
+    <img src="{{ absolute_url(asset('images/logo.png')) }}"
 
 The ``$message`` object supports many more options, such as including attachments,
 adding HTML content, and much more. Fortunately, Swift Mailer covers the topic