refactor(docker compose example): added in postgress stuff plus network

docker-compose-example.yml

@@ -7,9 +7,20 @@ services:
             no_cache: true
         image: git.tuffraid.net/cowch/logistics_support_tool:latest
         container_name: lst_backend
+        networks:
+            - docker-network
+        environment:
+            DB_HOST: postgres
+            DB_PORT: 5432
+            DB_USER: username
+            DB_PASSWORD: passwordl
+            DB_NAME: lst
         volumes:
             - /path/to/backend/data:/data
         ports:
             - "8080:8080"
         restart: unless-stopped
         pull_policy: never
+networks:
+    docker-network:
+        external: true