fixed intendation and shortened the link

Author: SrgSteak

cookbook/security/entity_provider.rst

@@ -585,8 +585,8 @@ The code below shows the implementation of the
 
 .. tip::
 
-   Don't forget to 
-   :ref: `add the repository class to the mapping definition of your entity <book-doctrine-custom-repository-classes>`.
+    Don't forget to add the repository class to the mapping definition of
+    :ref: ` your entity <book-doctrine-custom-repository-classes>`.
 
 To finish the implementation, the configuration of the security layer must be
 changed to tell Symfony to use the new custom entity provider instead of the