added demo-specific deployment environment and directives

docker-compose.override.yml

@@ -0,0 +1,10 @@
+---
+services:
+  cron:
+    image: bryanpedini/dockercron:${CRON_VERSION}
+    restart: unless-stopped
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+      - ${CRON_CRONTAB}:/crontab/root
+      - ${CRON_JOBS}:/jobs
+      - ${NYX_DEMO}:/opt/nyx