create a sub-heading for react-hook options

Author: ryan953

docs/product/sentry-toolbar/setup.mdx

@@ -98,6 +98,7 @@ The complete list of options is here:
 | `debug (optional)` | `string \| undefined` | A comma separated string of debug targets to enable. Example: `'logging,state'`. If the list contains 'all' or 'true' then all targets will be enabled. Valid targets: `'logging' 'login-success' 'settings' 'state'` | `undefined` |
 | `mountPoint (optional)` | `HTMLElement \| () => HTMLElement \| undefined` | Where to mount the Toolbar in the DOM. | `document.body` |
 
+### Extra Reack Hook Options
 
 The React hook supports some other top-level options. The defaults values are: