fixed both missing empty lines below tip

On 23.6.2013 20:39, Wouter J wrote:
>
> In cookbook/security/entity_provider.rst:
>
> >      }
> >
> > -To improve performances and avoid lazy loading of groups when retrieving a user
> > -from the custom entity provider, the best solution is to join the groups
> > +
> > +.. tip::
> > +    To generate missing setters and getters for your ``Role`` entity, you
>
> empty line is missing here too
>
> —
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> <https://github.com/symfony/symfony-docs/pull/2753/files#r4832866>.
>