docs(org): update README for new frontend system as default

Add new frontend system installation as the default path with package
discovery and extension configuration. Move old frontend system wiring
to an "Old Frontend System" section. Update README-alpha.md to be an
extension reference rather than experimental documentation.

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>
Made-with: Cursor

plugins/org/README-alpha.md

@@ -1,8 +1,6 @@
-# Org Plugin
+# Org Plugin - Extension Reference
 
-> [!WARNING]
-> This documentation is made for those using the experimental new Frontend system.
-> If you are not using the new frontend system, please go [here](./README.md).
+This page contains detailed documentation for all extensions provided by the `@backstage/plugin-org` plugin. For general information about the plugin, see the [README](./README.md).
 
 This is a plugin that extends the Catalog entity page with some users and groups overview cards:
 

plugins/org/README.md

@@ -1,8 +1,5 @@
 # Org Plugin for Backstage
 
-> Disclaimer:
-> If you are looking for documentation on the experimental new frontend system support, please go [here](./README-alpha.md).
-
 ## Features
 
 - Show Group Page
@@ -21,6 +18,33 @@ Here's an example of what the User Profile looks like:
 
 ![Group Page example](./docs/user-profile-example.png)
 
+## Installation
+
+```bash
+# From your Backstage root directory
+yarn --cwd packages/app add @backstage/plugin-org
+```
+
+Once installed, the plugin is automatically available in your app through the default package discovery. For more details and alternative installation methods, see [installing plugins](https://backstage.io/docs/frontend-system/building-apps/installing-plugins).
+
+You can enable entity cards on the catalog entity page through configuration:
+
+```yaml
+# app-config.yaml
+app:
+  extensions:
+    - entity-card:org/group-profile
+    - entity-card:org/members-list
+    - entity-card:org/ownership
+    - entity-card:org/user-profile
+```
+
+For the full list of available extensions and their configuration options, see the [README-alpha.md](./README-alpha.md).
+
+## Old Frontend System
+
+If your Backstage app uses the old frontend system, you need to manually wire the plugin into your app.
+
 ### MyGroupsSidebarItem
 
 The MyGroupsSidebarItem provides quick access to the group(s) the logged in user is a member of directly in the sidebar.