African Countries: A Curated Dataset on Africa Indicators for Education and Data Science

Documentation update - added DOI badge to README.md, updated CITATION.cff and version.txt. No changes to core dataset.文档更新说明：已为README.md文件添加数字对象标识符（DOI）徽章，更新了CITATION.cff与version.txt文件。核心数据集未作任何修改。