docs: Update README to document automatic numbering feature from issue #7

[Copilot]

This PR updates the README.md documentation to reflect the automatic numbering feature that was implemented in issue #7. The CSV format and user interface now include automatic sequential numbering for each study problem.

Changes Made

CSV Format Documentation

• Updated basic format from 質問,回答 to 番号,質問,回答
• Added examples showing automatic numbering (1, 2, 3, etc.)
• Updated usage examples to reference problem numbers instead of positions
• Documented backward compatibility with old CSV formats

Feature Documentation

• Added automatic numbering as a key feature in the main features list
• Updated data management section to highlight automatic number assignment
• Updated usage instructions to explain how numbers are automatically assigned
• Updated project structure to reflect numbering support in templates and datasets

Key Updates

• Main Features: Added "自動番号付け" as the first feature
• CSV Examples: All CSV format examples now show the numbering column
• Usage Instructions: Updated to explain automatic number assignment
• Range Specification: Changed from position-based to number-based references

Screenshot

The automatic numbering feature is now properly documented and matches the current implementation:

As shown in the screenshot, each problem displays a bold sequential number (1, 2, 3, etc.) in the first column of the data table, making it easy to identify and reference specific problems.

The documentation now accurately reflects the current state of the application with all the enhancements from issue #7.

Fixes #8.

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