Merge pull request #5332 from adamdmharvey/update-plugin-doco

docs: Update plugin example for composability

docs/getting-started/configure-app-with-plugins.md

@@ -31,26 +31,33 @@ CircleCI is a frontend UI plugin, it goes in `app` rather than `backend`.
 
 ```js
 // packages/app/src/plugins.ts
-export { plugin as Circleci } from '@backstage/plugin-circleci';
+export { plugin as CircleCi } from '@backstage/plugin-circleci';
 ```
 
-3. Register the plugin router:
+3. Register the plugin in the entity pages:
 
-```jsx
-// packages/app/src/components/catalog/EntityPage.tsx
+```diff
+ // packages/app/src/components/catalog/EntityPage.tsx
++import {
++  EntityCircleCIContent,
++  isCircleCIAvailable,
++} from '@backstage/plugin-circleci';
 
-import { Router as CircleCIRouter } from '@backstage/plugin-circleci';
-
-// Then somewhere inside <EntityPageLayout>
-<EntityPageLayout.Content
-  path="/ci-cd/*"
-  title="CI/CD"
-  element={<CircleCIRouter />}
-/>;
+...
+ const cicdContent = (
+   <EntitySwitch>
+     ...
++     <EntitySwitch.Case if={isCircleCIAvailable}>
++       <EntityCircleCIContent />
++     </EntitySwitch.Case>;
+   </EntitySwitch>
+ );
 ```
 
-Note that stand-alone plugins that are not "attached" to the Software Catalog
-would be added outside the `EntityPage`.
+This is just one example, but each Backstage instance may integrate content or
+cards to suit their needs on different pages, tabs, etc. Note that stand-alone
+plugins that are not "attached" to the Software Catalog would be added outside
+the `EntityPage`.
 
 4. [Optional] Add proxy config: