Add a Caption To an Existing Slide

## Can you think of a better caption?
Each slide can have more than one caption. Check out the current slide show and add a caption (or two).
If you need help, check out the Appendix in the training manual.

首先查看当前的幻灯片放映和培训手册中的附录，以了解现有的说明文字和预期样式。向现有幻灯片添加一条或两条说明文字，然后确认更新后的幻灯片显示正确，并且说明文字对其有所改善。

由索引模型根据 Issue 内容生成。