Don't track site specific configuration in the repository.

docker/environment.sh.template

@@ -1,6 +1,9 @@
 #!/usr/bin/env bash
 
-export ASTEROID_STREAM_URL='http://ice.asteroid.radio'
+# Ensure you copy this file to 'environment.sh' in this directory, and
+# change it to match your own stream configuration.
+
+export ASTEROID_STREAM_URL='http://localhost:8080'
 
 # source this file prior to starting the asteroid containers. Set the
 # DB name and access params here.