minor #4218 Caution that roles should start with ROLE_ (jrjohnson)

This PR was merged into the 2.3 branch.

Discussion
----------

Caution that roles should start with ROLE_

In order to save someone else a few hours of frustration make it clear that the ROLE_ preface is not just for show.

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

Commits
-------

749996b Fix reference label
f856641 Add label book-security-roles
9d13930 Add formatting, links, and clarity
1522de7 Caution that roles should start with ROLE_

Author: weaverryan

book/security.rst

@@ -1652,6 +1652,8 @@ the default for the firewall as a whole).
 For more information about user provider and firewall configuration, see
 the :doc:`/reference/configuration/security`.
 
+.. _book-security-roles:
+
 Roles
 -----
 

cookbook/security/entity_provider.rst

@@ -651,6 +651,14 @@ about in this section.
     If you fail to return any roles, it may appear as if your user isn't
     authenticated at all.
 
+.. caution::
+
+    In order to work with the security configuration examples on this page
+    all roles must be prefixed with ``ROLE_`` (see
+    the :ref:`section about roles <book-security-roles>` in the book). For
+    example, your roles will be ``ROLE_ADMIN`` or ``ROLE_USER`` instead of
+    ``ADMIN`` or ``USER``.
+
 In this example, the ``AcmeUserBundle:User`` entity class defines a
 many-to-many relationship with a ``AcmeUserBundle:Role`` entity class.
 A user can be related to several roles and a role can be composed of