Add a category for "probabilistic programming"

[BaxterEaves]

Hello,

I'd like to add our packages rv and Lace, but they don't fall neatly into any of the existing categories. We're a company dedicated to building probabilistic programming tools in rust, and we have a number of tools on the horizon that we'd like to list.

We also, have changepoint, which is a time series analysis crate, but could probably fit under probabilistic programming because it's based on Bayesian methodology.

Thanks!