chore: mention entityClient as an additional option of createRouter

.changeset/weak-otters-love.md

@@ -3,4 +3,14 @@
 '@backstage/plugin-scaffolder-backend': minor
 ---
 
-Scaffolder's API `/v1/jobs` will accept `templateName` instead of `template` Entity.
+`createRouter` of scaffolder backend will now require additional option as `entityClient` which could be generated by `CatalogEntityClient` in `plugin-scaffolder-backend` package. Here is example to generate `entityClient`.
+
+```js
+import { CatalogEntityClient } from '@backstage/plugin-scaffolder-backend';
+import { SingleHostDiscovery } from '@backstage/backend-common';
+
+const discovery = SingleHostDiscovery.fromConfig(config);
+const entityClient = new CatalogEntityClient({ discovery });
+```
+
+- Scaffolder's API `/v1/jobs` will accept `templateName` instead of `template` Entity.