minor symfony#9537 Symfony 4 Security: Added note, how to install profiler bundle (aurelijusb)

This PR was merged into the 4.0 branch.

Discussion
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Symfony 4 Security:  Added note, how to install profiler bundle

There is example picture (`_images/security/anonymous_wdt.png`) with `profiler` bundle,
but when creating Symfony 4 project with `flex` – `profiler` bundle is not included by default.

Therefore for new Symfony 4 users it is hard to follow documentation.

Commits
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45c5399 Added example, how to install profiler bundle

Author: wouterj

security.rst

@@ -127,6 +127,13 @@ be fooled by the "Yes" next to Authenticated, you're just an anonymous user:
 .. image:: /_images/security/anonymous_wdt.png
    :align: center
 
+.. tip::
+    If you do not see toolbar, it can be installed with :doc:`Profiler </profiler>` bundle
+
+    .. code-block:: terminal
+
+        $ composer require profiler --dev
+
 You'll learn later how to deny access to certain URLs or controllers.
 
 .. tip::