Update persisted form example README.md

Fix broken image path.

Author: thgaskell

examples/persisted-form/README.md

@@ -117,4 +117,4 @@ return (
 4. Construct your form using the `react-radfish` components. See the `/src/pages/Form.jsx` file to see how to construct the form and use the methods available from `FormWrapper`.
 
 # Persisted Form Example Preview
-![Persisted Form](./src/assets/persisted.png)
+![Persisted Form](./src/assets/persisted-form.png)