minor #7749 Reword the explanation about enabling validation and annotations (javiereguiluz)

This PR was merged into the 2.7 branch.

Discussion
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Reword the explanation about enabling validation and annotations

This fixes #7412.

Commits
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fee9949 Reword the explanation about enabling validation and annotations

Author: xabbuh

validation.rst

@@ -211,8 +211,9 @@ Inside the template, you can output the list of errors exactly as needed:
 Configuration
 -------------
 
-The Symfony validator is enabled by default, but you must explicitly enable
-annotations if you're using the annotation method to specify your constraints:
+Before using the Symfony validator, make sure it's enabled in the main config
+file. Besides, if you plan to use annotations to configure validation, make sure
+that the ``enable_annotations`` option is ``true``:
 
 .. configuration-block::