fix: update Dockerfile and documentation for APT_CACHER_NG configuration

README-Docker.md

@@ -58,7 +58,8 @@ This application is a Craigslist job scraper with a Flask web interface.
 ### Environment Variables
 
 - `FLASK_ENV`: Set to `production`
-- `FLASK_SECRET`: Secret key for Flask sessions
+- `FLASK_SECRET`: Secret key for Flask sessions (required)
+- `APT_CACHER_NG`: Optional URL for apt-cacher-ng proxy to speed up package downloads (e.g., `http://192.168.88.14:3142`)
 
 ### Database Configuration
 
@@ -309,6 +310,7 @@ services:
 
       # Optional configuration
       - GUNICORN_WORKERS=${GUNICORN_WORKERS:-4}
+      - APT_CACHER_NG=${APT_CACHER_NG}
     volumes:
       - type: bind
         source: ./cache