Fixed #27387 -- Doc'd required HTML attribute in Field.required docs.

docs/ref/forms/fields.txt

@@ -92,6 +92,15 @@ then ``clean()`` will return a *normalized* empty value rather than raising
 For other ``Field`` classes, it might be ``None``. (This varies from field to
 field.)
 
+Widgets of required form fields have the ``required`` HTML attribute. Set the
+:attr:`Form.use_required_attribute` attribute to ``False`` to disable it. The
+``required`` attribute isn't included on forms of formsets because the browser
+validation may not be correct when adding and deleting formsets.
+
+.. versionadded:: 1.10
+
+    Support for the ``required`` HTML attribute was added.
+
 ``label``
 ---------