Add README

README.md

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+# Docker service reporter 
+
+This is a small python script that will discover all running
+docker containers and store information about them in etcd.
+
+## Why?
+
+Having service details in shared storage such as etcd allows
+other processes to discover services, or automate configuration
+or administration tasks (such as configuring reverse proxies).
+
+## Usage
+
+The container requires access to the docker API, so you need
+to volume mount the docker socket:
+
+```bash
+docker run -d --name service-reporter \
+              --restart always \
+              -v /var/run/docker.sock:/var/run/docker.sock \ 
+              csmith/service-reporter:latest
+```
+
+## Schema
+
+The script stores values relating to containers, labels, and
+networks in etcd:
+
+```
+/docker/containers/{name}/image = "ubuntu:xenial"
+                         /labels/service = "foo"
+                         /labels/org.example.some-label = "bar"
+                         /net/addr/{network1} = "172.1.2.3"
+                                  /{network2} = "172.0.2.3"
+                             /ports/tcp/{container_port1} = {host_port} 
+                                       /{container_port2} = 0 # Not exposed
+                                   /udp/...
+
+/docker/labels/{label_1}/{container_name_1} = "foo"
+                        /{container_name_2} = "bar"
+              /{label_2}/...
+
+/docker/networks/{network1}/{container_name_1} = "172.1.2.3"
+                           /{container_name_2} = "172.0.2.3"
+                /{network2}/...
+```
+
+## Current known issues
+
+* The docker node is deleted when the script starts, so you can't run multiple
+  copies on multiple hosts
+* The script updates once and exits, instead of listening for events
+* There's no way to get notified when the script has finished, rather than
+  mid-update
+