add useOptimistic reference

Author: MaxwellCohen

src/content/reference/react-dom/components/form.md

@@ -342,9 +342,7 @@ export async function deliverMessage(message) {
 ```
 
 </Sandpack>
-
-[//]: # 'Uncomment the next line, and delete this line after the `useOptimistic` reference documentation page is published'
-[//]: # 'To learn more about the `useOptimistic` Hook see the [reference documentation](/reference/react/useOptimistic).'
+To learn more about the `useOptimistic` Hook see the [reference documentation](/reference/react/useOptimistic).
 
 ### Handle form submission errors {/*handling-form-submission-errors*/}