minor #5542 [Cookbook][Email] add missing versionadded directive (xabbuh)

This PR was merged into the 2.7 branch.

Discussion
----------

[Cookbook][Email] add missing versionadded directive

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.7+
| Fixed tickets | #4918

Commits
-------

bc880d0 add missing versionadded directive

Author: weaverryan

cookbook/email/email.rst

@@ -138,6 +138,11 @@ template might look something like this:
     {# Makes an absolute URL to the /images/logo.png file #}
     <img src="{{ absolute_url(asset('images/logo.png')) }}"
 
+.. versionadded:: 2.7
+    The ``absolute_url()`` function was introduced in Symfony 2.7. Prior
+    to 2.7, the ``asset()`` function has an argument to enable returning
+    an absolute URL.
+
 The ``$message`` object supports many more options, such as including attachments,
 adding HTML content, and much more. Fortunately, Swift Mailer covers the topic
 of `Creating Messages`_ in great detail in its documentation.