Use port 21000 and document CDN hostname requirements

deploy/docker-compose.yml

@@ -7,7 +7,7 @@ services:
     image: rawmark:local
     restart: unless-stopped
     ports:
-      - "0.0.0.0:${RAWMARK_PORT:-20080}:8080"
+      - "0.0.0.0:${RAWMARK_PORT:-21000}:8080"
     volumes:
       - ./data:/data
     stop_grace_period: 15s