The link to Zabbix Documentation Licence page is missing.
Also a link is rendered as "external", because a full URL is used. It should use relative path (without "www.zabbix.com" part) to be recognized as "internal" by the renderer. This will clearly show the user that she is not going to leave Zabbix documentation website by clicking the link.
I don't know if this is a good idea to manually maintain a list of children pages if there is an auto-generated sidebar anyway. Maybe worth removing this single link altogether.