doc: Document installation and distribution

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

Author: ChristophWurst

README.md

@@ -8,6 +8,16 @@ Detect and warn about suspicious IPs logging into Nextcloud
 
 The app is still under development, so it’s time for you to [get involved! 👩‍💻](https://github.com/nextcloud/suspicious_login#development-setup)
 
+## Installation
+
+### Nextcloud 25 and newer
+
+The app is [shipped](https://docs.nextcloud.com/server/latest/developer_manual/app_publishing_maintenance/release_process.html#shipped-apps) and comes with the installation of Nextcloud Server. No additional steps are necessary.
+
+### Nextcloud 24 and older
+
+The app is available through the [app store](https://apps.nextcloud.com/apps/suspicious_login). It can be [installed through Nextcloud's app management UI](https://docs.nextcloud.com/server/latest/admin_manual/apps_management.html#managing-apps).
+
 ## How it works
 
 ### Data collection