[docs-only] update ocis-hello (sourced from owncloud dev)

This change aligns with https://github.com/owncloud/ocis-hello/pull/138 where we have the same note.

```
**IMPORTANT:**
The `ocis-hello` example is currently under revision and does not work due to latest changes in master.
```

docs/ocis/deployment/ocis_hello.md

@@ -9,6 +9,9 @@ geekdocFilePath: ocis_hello.md
 
 {{< toc >}}
 
+**IMPORTANT:**
+The `ocis-hello` example is currently under revision and does not work due to latest changes in master.
+
 ## Overview
 
 - oCIS running behind Traefik as reverse proxy