Merge pull request #9456 from RoadieHQ/add-missing-step-to-migration-docs

add missing step to docs

docs/features/software-templates/migrating-from-v1beta2-to-v1beta3.md

@@ -34,6 +34,20 @@ The migration path is pretty simple, and we've removed some of the pain points
 from writing the `handlebars` templates too. Let's go through what's new and how
 to upgrade.
 
+## Add the Processor to the `plugin-catalog-backend`
+
+An important change is to add the required processor to your `packages/backend/src/plugins/catalog.ts`
+
+```diff
++import { ScaffolderEntitiesProcessor } from '@backstage/plugin-scaffolder-backend';
+
+...
+
+   const builder = await CatalogBuilder.create(env);
++  builder.addProcessor(new ScaffolderEntitiesProcessor());
+   const { processingEngine, router } = await builder.build();
+```
+
 ## `backstage.io/v1beta2` -> `scaffolder.backstage.io/v1beta3`
 
 The most important change is that you'll need to switch over the `apiVersion` in