Mount configuration read-only

docker-compose.yml.example

@@ -9,7 +9,7 @@ services:
     environment:
       - FABCAL_CACHE_EXPIRE=120
     volumes:
-      - ./config.yml:/app/config.yml
+      - ./config.yml:/app/config.yml:ro
     # use the line below when running this behind reverse proxy (only if it sets the proxy headers, though)
     #command: --proxy-headers --forwarded-allow-ips="*"