Update instructions in docker/README.md

docker/README.md

@@ -4,7 +4,7 @@ This is a sample configuration for running Healthchecks with
 [Docker](https://www.docker.com) and [Docker Compose](https://docs.docker.com/compose/).
 
 **Note: The Docker configuration is a recent addition, and, for the time being,
-should be considered highly experimental**.
+should be considered as highly experimental**.
 
 Note: For the sake of simplicity, the sample configuration starts a single database
 node and a single web server node, both on the same host. It also does not handle SSL
@@ -13,8 +13,13 @@ SSL-terminating load balancer or reverse proxy in front of it.
 
 ## Getting Started
 
-* Edit the `docker-compose.yml` file; add your SMTP credentials
-  and any other needed environment variables.
+* Add your configuration in the `/docker/.env` file.
+  As a minimum, set the following fields:
+    * `DEFAULT_FROM_EMAIL` – the "From:" address for outbound emails
+    * `EMAIL_HOST` – the SMTP server
+    * `EMAIL_HOST_PASSWORD` – the SMTP password
+    * `EMAIL_HOST_USER` – the SMTP username
+    * `SECRET_KEY` – secures HTTP sessions, set to a random value
 * Create and start containers:
 
         $ docker-compose up