Properly attribute code taken from wandb

[matthewfeickert]

As properly pointed out by @rct225 (:bow:), the code that was added from wandb in PR #15 is under the MIT License and to properly attribute that code we should

attribute the original author for the parts [we] incorporated and include a copy of the MIT License terms

I'm not 100% on if we actually need to add the MIT Licence into the LICENSE file as I think that Apache 2.0 meets all the requirements for MIT (@lukasheinrich? @kratsg?), but we definitely need to attribute the code to wandb.