Add doc for the escape_label option

Author: Dinduks

reference/forms/types/field.rst

@@ -22,3 +22,5 @@ The ``field`` type predefines a couple of options:
 .. include:: /reference/forms/types/options/attr.rst.inc
 
 .. include:: /reference/forms/types/options/translation_domain.rst.inc
+
+.. include:: /reference/forms/types/options/escape_label.rst.inc

reference/forms/types/options/escape_label.rst.inc

@@ -0,0 +1,14 @@
+escape_label
+~~~~~~~~~~~~
+**type**: ``Boolean``  **default**: ``true``
+
+If set to false, the label's content won't be escaped. This option is useful when wanting to use HTML tags inside a label.
+
+.. code-block:: php
+
+    $builder->add('acceptRules', 'checkbox', array(
+        'label'        => '<strong>I accept the rules</strong>',
+        'escape_label' => false,
+    ));
+
+