minor symfony#3845 added link to /cookbook/security/force_https. (aitboudad)

This PR was merged into the 2.3 branch.

Discussion
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added link to /cookbook/security/force_https.

| Q             | A
| ------------- | ---
| Doc fix?	 | yes
| New docs? | no
| Applies to | all
|Fixed tickets |	-

Commits
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517d54e added link to /cookbook/security/force_https.

Author: weaverryan

cookbook/routing/scheme.rst

@@ -69,4 +69,5 @@ to always use ``http``.
     The Security component provides another way to enforce HTTP or HTTPS via
     the ``requires_channel`` setting. This alternative method is better suited
     to secure an "area" of your website (all URLs under ``/admin``) or when
-    you want to secure URLs defined in a third party bundle.
+    you want to secure URLs defined in a third party bundle (see
+    :doc:`/cookbook/security/force_https` for more details).