minor #6016 Corrected the line references for the basic controller example (theTeddyBear)

This PR was submitted for the 2.8 branch but it was merged into the 2.3 branch instead (closes #6016).

Discussion
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Corrected the line references for the basic controller example

| Q             | A
| ------------- | ---
| Doc fix?          | yes
| New docs?     |no
| Applies to    | 2.8+
| Fixed tickets | n/a

Corrected the line references for the basic controller example; added a reference to separate use statement from initial namespacing explanation.

Commits
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82a1808 Corrected the line references for the basic controller example; added a reference to separate use statement from initial namespacing explanation.

Author: wouterj

book/controller.rst

@@ -116,8 +116,10 @@ Controllers are also called *actions*.
 
 This controller is pretty straightforward:
 
-* *line 4*: Symfony takes advantage of PHP's namespace functionality to
-  namespace the entire controller class. The ``use`` keyword imports the
+* *line 2*: Symfony takes advantage of PHP's namespace functionality to
+  namespace the entire controller class.
+
+* *line 4*: Symfony again takes advantage of PHP's namespace functionality: the ``use`` keyword imports the
   ``Response`` class, which the controller must return.
 
 * *line 6*: The class name is the concatenation of a name for the controller