message: Add `addProcessor` code sample to external-integrations
diff: @@ -156,8 +156,18 @@ The key points to note are:
  - Call `emit` any number of times with the results of that process
  - Finally return `true`
  -You should now be able to instantiate this class in your backend, and add it to
  -the `CatalogBuilder` using the `addProcessors` method.
  +You should now be able to add this class to your backend in
  +`packages/backend/src/plugins/catalog.ts`:
  +
  +```diff
  ++ import { SystemXReaderProcessor } from '../path/to/class';
  +
  +export default async function createPlugin(
  + env: PluginEnvironment,
  +): Promise<Router> {
  + const builder = new CatalogBuilder(env);
  ++ builder.addProcessor(new SystemXReaderProcessor(env.reader));
  +```
  Start up the backend - it should now start reading from the previously
  registered location and you'll see your entities start to appear in Backstage.
  