docs: add instructions to readmes

Signed-off-by: secustor <sebastian@poxhofer.at>

plugins/catalog-unprocessed-entities/README.md

@@ -52,16 +52,22 @@ Import `catalogUnprocessedEntitiesPlugin` in your `App.tsx` and add it to your a
 
 ```typescript
 import catalogUnprocessedEntitiesPlugin from '@backstage/plugin-catalog-unprocessed-entities';
-
-// ...
+import { unprocessedEntitiesDevToolsRoute } from '@backstage/plugin-catalog-unprocessed-entities/alpha';
 
 export const app = createApp({
   features: [
+    appFeature,
     // ...
     catalogUnprocessedEntitiesPlugin,
     // ...
   ],
 });
+
+// Optionally add unprocessed entities route to devtools
+const appFeature = createFrontendModule({
+  pluginId: 'app',
+  extensions: [unprocessedEntitiesDevToolsRoute],
+});
 ```
 
 ## Customization

plugins/devtools/README.md

@@ -160,6 +160,33 @@ You can also add tabs to show content from other plugins that fit well with the
 
 #### Catalog Unprocessed Entities Tab
 
+##### New Frontend System
+
+Create an extension and/or load a 3rd party extension to add additional tabs.
+
+```tsx
+import { DevToolsRouteBlueprint } from '@backstage/plugin-devtools-react';
+
+export const unprocessedEntitiesDevToolsRoute = DevToolsRouteBlueprint.make({
+  params: {
+    path: 'unprocessed-entities',
+    title: 'Unprocessed Entities',
+    loader: () =>
+      import('../components/UnprocessedEntities').then(
+        ({ UnprocessedEntitiesContent }) =>
+          createElement(UnprocessedEntitiesContent),
+      ),
+  },
+});
+
+const appFeature = createFrontendModule({
+  pluginId: 'app',
+  extensions: [unprocessedEntitiesDevToolsRoute],
+});
+```
+
+##### Old System
+
 Here's how to add the Catalog Unprocessed Entities tab:
 
 1. Install and setup the [Catalog Unprocessed Entities plugin](https://github.com/backstage/backstage/tree/master/plugins/catalog-unprocessed-entities) as per its documentation