Added the missing versionadded directive

Author: javiereguiluz

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

@@ -3,6 +3,10 @@
 
 **type**: ``bool`` **default**: ``false``
 
+.. versionadded:: 5.1
+
+	The ``label_html`` option was introduced in Symfony 5.1.
+
 By default, the contents of the ``label`` option are escaped before rendering
 them in the template. Set this option to ``true`` to not escape them, which is
 useful when the label contains HTML elements.