Add A New Slide

## We Need More Slides
Grab another octocat and create a new slide from scratch.
If you need help, check out the Appendix in the training manual.

Start with the Appendix in the training manual, then inspect the repository's existing slide structure and available octocat assets. Add one new slide consistent with those materials and verify that it appears with the existing slides.

索引モデルが issue の本文から書いたものです。