docs(icinga-version): update README

Author: danyalberchtoldlf

check-plugins/icinga-version/README.md

@@ -81,6 +81,12 @@ Icinga v2.14.6 (EOL unknown)
 | icinga-version | Number | Installed Icinga version as float. "2.14.6" becomes "2.146". |
 
 
+## Troubleshooting
+
+`Error running sudo -u \#48 /var/www/html/nextcloud/occ config:list: rc=1 sudo: /var/www/html/nextcloud/occ: command not found`:
+Permission for `/var/www/html/nextcloud/occ` must be `0755`.
+
+
 ## Credits, License
 
 * Authors: [Linuxfabrik GmbH, Zurich](https://www.linuxfabrik.ch)