minor #4399 Explain form() and form_widget() in form customization (oopsFrogs, WouterJ)

This PR was merged into the 2.3 branch.

Discussion
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Explain form() and form_widget() in form customization

Continues #4365

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

Original PR description:

> In the Form chapter of Book for Symfony 2.3, we use `{{ form(form) }}` to render the entire form ( in contrast to `{{ form_widget(form) }}` for older version of Symfony ). so maybe it should use `{{ form(form) }}` here for consistency.

Commits
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0086c5e Applied suggestion by Ryan
d653ff4 Update form_customization.rst

Author: weaverryan

cookbook/form/form_customization.rst

@@ -67,11 +67,19 @@ just one line:
 
     .. code-block:: jinja
 
+        {# renders all fields #}
         {{ form_widget(form) }}
 
+        {# renders all fields *and* the form start and end tags #}
+        {{ form(form) }}
+
     .. code-block:: php
 
-        <?php echo $view['form']->widget($form); ?>
+        <!-- renders all fields -->
+        <?php echo $view['form']->widget($form) ?>
+
+        <!-- renders all fields *and* the form start and end tags -->
+        <?php echo $view['form']->form($form) ?>
 
 The remainder of this recipe will explain how every part of the form's markup
 can be modified at several different levels. For more information about form