Docs: Add note about docker volume deletion in README files，will be more novice-friendly (#5133)

### What problem does this PR solve?


Docs: Add note about docker volume deletion in README files
refer to this question:
https://github.com/infiniflow/ragflow/issues/5132
### Type of change

- [x] Documentation Update

---------

Co-authored-by: wenju.li <wenju.li@deepctr.cn>
Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>
Co-authored-by: writinwaters <93570324+writinwaters@users.noreply.github.com>

README_ko.md

@@ -220,6 +220,7 @@ RAGFlow 는 기본적으로 Elasticsearch 를 사용하여 전체 텍스트 및
    ```bash
    $docker compose-f docker/docker-compose.yml down -v
    ```
+   Note: `-v` 는 docker 컨테이너의 볼륨을 삭제하고 기존 데이터를 지우며, 이 작업은 컨테이너를 중지하는 것과 동일합니다.
 2. **docker/.env**의 "DOC_ENGINE" 을 "infinity" 로 설정합니다.
 3. 컨테이너 부팅:
    ```bash