minor #6911 Article about logout. (BorodinDemid)

This PR was submitted for the 3.1 branch but it was merged into the 2.7 branch instead (closes #6911).

Discussion
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Article about logout.

In this lesson, we go through the authorization HTTP BASIC. I have tried to use this example and in the end got the exact same error again and again. The Internet has a lot of open topics about this. Like many other people, I have scroll lesson up to understand where I made a mistake. I think you need to specify that this is not a working example (in this context) it will save a lot of time people who study it.

Commits
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c64ca7a Article about logout.

security.rst

@@ -1102,6 +1102,14 @@ key:
 Logging Out
 -----------
 
+.. caution::
+
+    Notice that when using http-basic authenticated firewalls, there is no
+    real  way to log out : the only way to *log out* is to have the browser
+    stop sending your name and password  on every request. Clearing your
+    browser cache or restarting your browser usually helps. Some web developer
+    tools might be helpful here too.
+
 Usually, you'll also want your users to be able to log out. Fortunately,
 the firewall can handle this automatically for you when you activate the
 ``logout`` config parameter:
@@ -1202,14 +1210,6 @@ is defined by the ``target`` parameter above (e.g. the ``homepage``).
     :class:`Symfony\\Component\\Security\\Http\\Logout\\LogoutSuccessHandlerInterface`.
     See :doc:`Security Configuration Reference </reference/configuration/security>`.
 
-.. caution::
-
-    Notice that when using http-basic authenticated firewalls, there is no
-    real  way to log out : the only way to *log out* is to have the browser
-    stop sending your name and password  on every request. Clearing your
-    browser cache or restarting your browser usually helps. Some web developer
-    tools might be helpful here too.
-
 .. _security-role-hierarchy:
 
 Hierarchical Roles