Extend documentation

Author: arnested

README.md

@@ -16,3 +16,52 @@ The server will answer with the following HTTP status codes:
 * 503 Internal Server error: If the system is in any other state
 * 500 Service Unavailable: If the HTTP server got an error while requesting the system state
 * 410 Gone: If it cannot connect to the systemd bus
+
+## What is the purpose of this?
+
+This is a "poor mans" monitoring solution.
+
+It has been created to expose the overall system state to monitoring
+solutions such as [Pingdom](https://www.pingdom.com/) or
+[StatusCake](https://www.statuscake.com/).
+
+## Docker image
+
+There is a [Docker image at Docker
+Hub](https://hub.docker.com/r/arnested/systemd-state/).
+
+## The status is not protected by HTTPS or authentication
+
+You are right. It is exposed on HTTP without any authentication. I
+have chosen the same stance as Prometheus on this. See [Prometheus'
+FAQ](https://prometheus.io/docs/introduction/faq/#why-don-t-the-prometheus-server-components-support-tls-or-authentication-can-i-add-those).
+
+Personally I have placed systemd-state behind
+[Træfik](https://traefik.io) with basic authentication.
+
+## Example docker-compose configuration with traefik
+
+Exposing the status on https://example.com/_systemd:
+
+```yml
+version: "2"
+
+services:
+  systemd:
+    image: arnested/systemd-state
+    volumes:
+      - '/run/systemd/private:/run/systemd/private:ro'
+    restart: always
+    labels:
+      - 'traefik.frontend.auth.basic=foo:$$apr1$$WCYo2XY2$$7PDdo922necZuGkMAeTI70'
+      - "traefik.port=80"
+      - "traefik.enable=true"
+      - "traefik.frontend.rule=Host:example.com;Path:/_systemd"
+    networks:
+      - web
+
+networks:
+  web:
+    external:
+      name: traefik_webgateway
+```