docs: update plugin installation docs

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/lighthouse/README.md

@@ -31,26 +31,17 @@ When you have an instance running that Backstage can hook into, first install th
 $ yarn add @backstage/plugin-lighthouse
 ```
 
-Then make sure to export the plugin in
-your app's [`plugins.ts`](https://github.com/backstage/backstage/blob/master/packages/app/src/plugins.ts)
-to enable the plugin:
-
-```js
-export { plugin as LighthousePlugin } from '@backstage/plugin-lighthouse';
-```
-
-Modify your app routes in `App.tsx` to include the Router component exported from the plugin, for example:
+Modify your app routes in `App.tsx` to include the `LighthousePage` component exported from the plugin, for example:
 
 ```tsx
 // At the top imports
-import { Router as LighthouseRouter } from '@backstage/plugin-lighthouse';
+import { LighthousePage } from '@backstage/plugin-lighthouse';
 
-// Inside App component
-<Routes>
+<FlatRoutes>
   // ...
-  <Route path="/lighthouse/*" element={<LighthouseRouter />} />
+  <Route path="/lighthouse" element={<LighthousePage />} />
   // ...
-</Routes>;
+</FlatRoutes>;
 ```
 
 Then configure the `lighthouse-audit-service` URL in your [`app-config.yaml`](https://github.com/backstage/backstage/blob/master/app-config.yaml).