Add crate: dfdx

[coreylowman]

Please add crate to category: Neural Networks

If you're open to multiple categories, I think dfdx could also be added to Reinforcement Learning (I have some examples of a Deep Q Network and Proximal Policy Optimization).

github: https://github.com/coreylowman/dfdx crates.io: https://crates.io/crates/dfdx docs.rs: https://docs.rs/dfdx/latest/dfdx/