explain app installation and app store restriction in README

nextcloud-onlyoffice/README.md

@@ -7,6 +7,24 @@ its document editor. Depends on the
 chart](https://open.greenhost.net/openappstack/nextcloud/tree/master/onlyoffice-documentserver).
 For configuration details on those charts, refer to their documentation.
 
+## Apps
+
+The Nextcloud app store allows admin users to install applications, many of
+which have not undergone security testing. For that reason we disabled
+downloading new apps via the app store. As the person installing Nextcloud it is
+possible to specify which applications from the app store are available for
+installation. It is also possible to enable them by default. Apps that are not
+enabled by default can be enabled through the Apps screen in Nextcloud.
+
+To install apps, edit the values.yaml file:
+
+```yaml
+apps:
+  - name: sociallogin  # Installs sociallogin app
+    enabled: false     # Disables sociallogin by default
+```
+
+
 ## Installation
 
 Make sure you have a `onlyoffice-documentserver` helm repo before running helm