Improve the README

## Do you have a favorite Git Resource?
Add it to the README!
If you need help, check out the Appendix in the training manual.

Open the README and review the existing Git resources. Use the Appendix in the training manual for guidance if needed, then add one favorite Git resource to the README. Done means the resource appears clearly in the README.

由索引模型根据 Issue 内容生成。