message: update README in user settings plugin to introduce UserSettingsTab
diff: @@ -69,17 +69,21 @@ const AppRoutes = () => (
  By default, the plugin renders 3 tabs of settings; GENERAL, AUTHENTICATION PROVIDERS, and FEATURE FLAGS.
  If you want to add more options for your users,
  -just pass the extra tabs as children of the `UserSettingsPage` route
  -where the children of that route represents the title of the tab.
  +just pass the extra tabs using `UserSettingsTab` components as children of the `UserSettingsPage` route.
  The path is in this case a child of the settings path,
  in the example below it would be `/settings/advanced` so that you can easily link to it.
  ```tsx
  +import {
  + UserSettingsPage,
  + UserSettingsTab,
  +} from '@backstage/plugin-user-settings';
  +
  <Route path="/settings" element={<UserSettingsPage />}>
  - <Route path="/advanced" element={<AdvancedSettings />}>
  - Advanced
  - </Route>
  -</Route>
  + <UserSettingsTab path="/advanced" title="Advanced">
  + <AdvancedSettings />
  + </UserSettingsTab>
  +</Route>;
  ```
  To standardize the UI of all setting tabs,
  