message: update doc around watch API with useFieldArray
diff: @@ -517,11 +517,18 @@ export default {
  </li>
  <li>
  <p>
  - However, if <code>defaultValues</code> was initialised in{" "}
  + If <code>defaultValues</code> was initialised in{" "}
  <code>useForm</code> as an argument, then the first render will
  return what's provided in <code>defaultValues</code>.
  </p>
  </li>
  + <li>
  + <p>
  + For <code>useFieldArray</code>, when all inputs get removed will
  + return <code>defaultValues</code>, you can walk around this issue
  + by checking <code>fields.length</code>.
  + </p>
  + </li>
  </ul>
  </>
  ),
  