message: update doc on handleSubmit
diff: @@ -989,7 +989,7 @@ handleSubmit(async (data) => await fetchAPI(data))`}
  <p>
  During the callback, if the function itself throws an error inside
  of <code>handleSubmit</code>, it will not swallow the error itself
  - but bubble up the error and <code>isSubmitSuccessful</code> will
  + but bubble it up instead and <code>isSubmitSuccessful</code> will
  be remained as <code>false</code>.
  </p>
  