Update bootstrap4.rst

ThomasLandauer · web-flow · commit f6ec9f7c1480 · 2021-04-13T21:28:15.000+02:00
diff --git a/form/bootstrap4.rst b/form/bootstrap4.rst
@@ -127,7 +127,7 @@ Appending an Asterisk to Required Fields
 
 Since form errors are rendered *inside* the ``<label>``, you cannot use CSS ``:after``
 to append an asterisk to the label, cause it would be displayed after the error message.
-Use 
+Use _`reference-form-option-label-html`_
 
 .. code-block:: twig
 
