minor #4702 Clarify tip for creating a new AppBundle (xelaris)

This PR was merged into the 2.3 branch.

Discussion
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Clarify tip for creating a new AppBundle

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

The tip seems to be confusing, since the AppBundle is also generated with `symfony new blog 2.3.23` (and 2.5.8). In addition the mentioned `generate:bundle` command does not work in SF 2.3 SE, since it stops with a `The namespace must contain a vendor namespace` error.

Commits
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7b9d583 Clarify tip for creating a new AppBundle

best_practices/creating-the-project.rst

@@ -152,8 +152,7 @@ that follows these best practices:
 
 .. tip::
 
-    If you are using Symfony 2.6 or a newer version, the ``AppBundle`` bundle
-    is already generated for you. If you are using an older Symfony version,
+    If your Symfony installation doesn't come with a pre-generated ``AppBundle``,
     you can generate it by hand executing this command:
 
     .. code-block:: bash