Add dfdx to crates

[coreylowman]

Do I need to add anything else like links to github or crates.io?

[anowell]

@coreylowman This just failed CI:

unknown variant `reinforcement-learning`, expected one of `scientific-computing`, `gpu-computing`, `neural-networks`, `metaheuristics`, `data-preprocessing`, `data-structures`, `clustering`, `decision-trees`, `linear-classifiers`, `reinforcement`, `nlp` at line 114 column 31

Once that's corrected, it can be merged.

[coreylowman]

Thanks @anowell, should be fixed now!

[anowell]

Thanks. Merged.