docs: add Maintenant to Monitoring section (#1276)

Maintenant is a self-discovering infrastructure monitoring tool
for Docker and Kubernetes with endpoint monitoring, heartbeats,
TLS certificates, resource metrics, and update intelligence.

README.md

@@ -197,6 +197,7 @@ _Source:_ [What is Docker](https://www.docker.com/why-docker/)
 
 - [InfluxDB, cAdvisor, Grafana](https://github.com/vegasbrianc/docker-monitoring) :ice_cube: - InfluxDB Time series DB in combination with Grafana and cAdvisor.
 - [Logspout](https://github.com/gliderlabs/logspout) :ice_cube: - Log routing for Docker container logs.
+- [Maintenant](https://github.com/kolapsis/maintenant) - Self-discovering infrastructure monitoring for Docker and Kubernetes. Auto-detects containers via labels, with endpoint monitoring, heartbeats, TLS certificates, resource metrics, update intelligence, and a built-in status page. Single binary with embedded SPA. By [kolapsis](https://github.com/kolapsis).
 - [monit-docker](https://github.com/decryptus/monit-docker) :ice_cube: - Monitor docker containers resources usage or status and execute docker commands or inside containers. [decryptus][decryptus].
 - [NexClipper](https://github.com/NexClipper/NexClipper) :ice_cube: - NexClipper is the container monitoring and performance management solution specialized in Docker, Apache Mesos, Marathon, DC/OS, Mesosphere, Kubernetes.
 - [Out-of-the-box Host/Container Monitoring/Logging/Alerting Stack](https://github.com/uschtwill/docker_monitoring_logging_alerting) :ice_cube: - Docker host and container monitoring, logging and alerting out of the box using cAdvisor, Prometheus, Grafana for monitoring, Elasticsearch, Kibana and Logstash for logging and elastalert and Alertmanager for alerting. Set up in 5 Minutes. Secure mode for production use with built-in [Automated Nginx Reverse Proxy (jwilder's)][nginxproxy].