message: Added `defaultValue` to useFieldArray example
  The current docs as misleading when they should `append({ name: "test" })` as if the initial value of the input would be `"test"`, while if no `defaultValue` is added to the input, the newly appended input will be empty by default.
diff: @@ -14,7 +14,7 @@ function App() {
  <ul>
  {fields.map((item, index) => (
  <li key={item.id}>
  - <input name={\`test[\${index}].name\`} ref={register()} />
  + <input name={\`test[\${index}].name\`} defaultValue={item.name} ref={register()} />
  <button onClick={() => remove(index)}>Delete</button>
  </li>
  ))}
  