bug symfony#8794 Add command to require Symfony security (Holicz, weaverryan)

This PR was merged into the 4.0 branch.

Discussion
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Add command to require Symfony security

The command should be there, because if someone unfamiliar with new Symfony structure use it, it will not work.

Commits
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202740b rewording
7d95e12 Add command to require Symfony security

Author: weaverryan

security/entity_provider.rst

@@ -36,6 +36,12 @@ and :ref:`user serialization to the session <security-serialize-equatable>`
 1) Create your User Entity
 --------------------------
 
+Before you begin, first make sure you install the Security component:
+
+.. code-block:: terminal
+
+    $ composer require security
+    
 For this entry, suppose that you already have a ``User`` entity inside an
 ``AppBundle`` with the following fields: ``id``, ``username``, ``password``,
 ``email`` and ``isActive``::