message: frontend/README: update instructions for adding plugin
diff: @@ -70,7 +70,13 @@ In [packages/app/src/plugins.ts](frontend/packages/app/src/plugins.ts), add the
  export { default as MyPlugin } from '@spotify-backstage/plugin-my-plugin';
  ```
  -You should now be able to see the default plugin page at [localhost:3000/my-plugin](http://localhost:3000/my-plugin) if you're serving the frontend.
  +To apply the above changes, go to the `frontend/` directory and run:
  +
  +```
  +$ yarn
  +```
  +
  +Now start or restart `yarn start`, and you should be able to see the default page for your new plugin at [localhost:3000/my-plugin](http://localhost:3000/my-plugin).
  ## Protobuf Definitions
  