updated install guide

DOCKER_SETUP.md

@@ -14,6 +14,7 @@ This setup uses `serversideup/php:8.4-fpm-nginx` as the base image and is design
     ```bash
     git clone https://github.com/pixelfed/pixelfed
     cd pixelfed
+    sudo chown -R www-data:www-data storage/ bootstrap/cache/
     ```
 
 1. **Copy the environment file:**