prometheus: add source code URL, license, language

- ref. https://github.com/awesome-foss/awesome-sysadmin/issues/416

README.md

@@ -509,7 +509,7 @@ _See also: [awesome-selfhosted/Database Management](https://github.com/awesome-s
 - [Performance Co-Pilot](http://pcp.io) - Lightweight, distributed system performance and analysis framework.
 - [PHP Server Monitor](https://www.phpservermonitor.org/) - Open source tool to monitor your servers and websites. ([Source Code](https://github.com/phpservermon/phpservermon))
 - [PhpSysInfo](https://phpsysinfo.github.io/phpsysinfo/) - A customizable PHP script that displays information about your system nicely. ([Source Code](https://github.com/phpsysinfo/phpsysinfo))
-- [Prometheus](https://prometheus.io/) - Service monitoring system and time series database.
+- [Prometheus](https://prometheus.io/) - Service monitoring system and time series database. ([Source Code](https://github.com/prometheus/prometheus)) `Apache-2.0` `Go`
 - [pyDash](https://k3oni.github.io/pydash/) - Small web-based monitoring dashboard for linux. ([Source Code](https://gitlab.com/k3oni/pydash))
 - [Riemann](http://riemann.io/) - Flexible and fast events processor allowing complex events/metrics analysis. ([Source Code](https://github.com/riemann/riemann))
 - [rtop](https://github.com/rapidloop/rtop) - an interactive, remote system monitoring tool based on SSH. ([Source Code](https://github.com/rapidloop/rtop))