Adding typst-slides to the offical packages repository

[jlduu]

Typst has added support for packages through a Github repository, so it's probably a good idea to add this template as an official package.

[ivaquero]

In fact, there's another fontawesome package which is based on unicode in the official repository. However, this repo is dependent on local svg. The dependency is kind of heavy, and does not fit for the online app, so I wonder if it can be accepted by the official repo.

I will try to make a PR recently.

Thanks for your interest.

[ivaquero]

I tried to make a PR, but this package doesn't suit the official repo.
typst/packages#310