Update Expression constraint with "pass" option

Author: Florent Mata

reference/constraints/Expression.rst

@@ -143,6 +143,11 @@ expression that must return true in order for validation to pass. To learn
 more about the expression language syntax, see
 :doc:`/components/expression_language/syntax`.
 
+.. note::
+
+    Alternatively, you can set the `pass`_ option to ``true`` in order to
+    assert that the expression must return true for validation to fail.
+
 .. sidebar:: Mapping the Error to a Specific Field
 
     You can also attach the constraint to a specific property and still validate