Update README.md

added xymon to "Monitoring" section.

README.md

@@ -512,6 +512,7 @@ _Related: [Metrics & Metric Collection](#metrics--metric-collection)_
 - [Status](https://github.com/dani3l0/Status) - Simple and lightweight system monitoring tool for small homeservers with a pleasant web interface. ([Demo](https://status.enshittification.social/) `MIT` `Python`
 - [Thruk](https://www.thruk.org/) - Multibackend monitoring web interface with support for Naemon, Nagios, Icinga and Shinken. ([Source Code](https://github.com/sni/Thruk)) `GPL-1.0` `Perl`
 - [Wazuh](https://wazuh.com/) - Unified XDR and SIEM protection for endpoints and cloud workloads. ([Source Code](https://github.com/wazuh/wazuh)) `GPL-2.0` `C`
+- [xymon](https://xymon.sourceforge.io/) - Monitoring tool for servers and networks. ([Source_Code](https://sourceforge.net/p/xymon/code/HEAD/tree/)) `GPL-2.0` `Perl/C/Shell`
 - [Zabbix](https://www.zabbix.com/) - Enterprise-class software for monitoring of networks and applications. ([Source Code](https://git.zabbix.com/projects/ZBX/repos/zabbix/browse)) `GPL-2.0` `C`