[minor] fixed code formatting doc

[min-xu-et]

Motivation

Improve doc.

Modification

• the doc was missing code block quotes, fixed.

Checklist

1. Ensure pre-commit pre-commit run --all-files or other linting tools are used to fix potential lint issues.
2. Confirm that modifications are covered by complete unit tests. If not, please add more unit tests for correctness.
3. Modify documentation as needed, such as docstrings or example tutorials.