Categories are "lightweight" in Jekyll, that is, rather than being fixed in a config file or list somewhere, they are created from scraping the YAML front matter from all the posts (and pages?).
I kind of don't like that because I also want to include descriptions for categories. So that my page will look basically like (pretend has reasonable HTML/CSS)
General
For stuff
Personal
For boring stuff
I would like to specify the descriptions fixed somewhere. I'm figuring out how to hack that with Jekyll bootstrap using their custom categories but the liquid is a bit dense so we'll see.