Add categories to the package meta data

[jeltz]

This should make the package easier to discover in the typst package universe.

[andreasKroepelin]

Great idea! I think I would add even more like beamer, slides, talk etc. Maybe we can brainstorm some.

[jeltz]

You can see what other libraries have used:

https://github.com/touying-typ/touying/blob/main/typst.toml

keywords = ["presentation", "slides", "lecture", "touying"]
categories = ["presentation"]

https://github.com/skriptum/diatypst/blob/main/typst.toml

keywords = ["slides", "presentation", "beamer", "quarto"]
categories = ["presentation"]

https://typst.app/universe/package/minideck

keywords = ["slides", "presentation", "dynamic", "pause"]
categories = ["presentation"]