Update the README

README.md

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 Ember lightning hosting for https://github.com/ember-cli/ember-cli-deploy
 
 [![Deploy](https://www.herokucdn.com/deploy/button.svg)](https://heroku.com/deploy?template=https://github.com/philipheinser/ember-lightning)
+
+# Docker support
+
+ember-lightning is also available as a docker container. To build the container run:
+
+```shell
+docker build --tag ember-lightning .
+```
+
+Then, to serve an ember-cli application run the container:
+
+```shell
+docker run --name $APP_NAME --env APP_NAME=$APP_NAME --env REDIS_SERVER=your-redis-server.example.com ember-lightning:latest
+```
+
+The image responds to these environment variables:
+
+### `APP_NAME`
+
+The name of the application as deployed in Redis.
+
+### `REDIS_SERVER`
+
+The hostname of the Redis server where ember-cli applications are deployed.
+This default to `redis` and so it is also possible to use Docker container
+links to connect the ember-lightning container to a running Redis container.
+
+### `REDIS_PORT`
+
+The port that Redis is listening on. Defaults to 6379. This only needs to be
+set if Redis is listening on a non-default port.
+
+### `REDIS_SECRET`
+
+The shared secret to use for authenticating to Redis. It is blank by default,
+which disables authentication.