added demo-specific deployment environment and directives

env.example

@@ -20,3 +20,10 @@ DIUN_EXCLUDE=
 # Nyx
 NYX_VERSION=latest
 NYX_DATA=./data
+NYX_DEMO=/path/to/nyx-demo
+# ^ where your docker-compose.override.yml resides for the demo deployment
+
+# Cron
+CRON_VERSION=1.0-alpine3.16
+CRON_CRONTAB=./crontab
+CRON_JOBS=./jobs