Add documentation for the Uncertain type

[marvin-hansen]

The recently added Uncertain type and its integration in DeepCausality need some documentation on the website.

Uncertain crate
https://github.com/deepcausality-rs/deep_causality/tree/main/deep_causality_uncertain

DeepCausality integraiton:
https://github.com/deepcausality-rs/deep_causality/blob/main/deep_causality/src/traits/causable_collection/collection_reasoning/collection_reasoning_uncertain.rs

https://github.com/deepcausality-rs/deep_causality/blob/main/deep_causality/src/traits/causable_collection/collection_reasoning/collection_reasoning_mixed.rs