Fix warning produced by cargo doc

[sunjay]

warning: Pattern matching for Cargo's include/exclude fields is changing and file `docs/README.md` WILL be included in a future Cargo version.
See https://github.com/rust-lang/cargo/issues/4268 for more info

To produce this warning, clone this repository and run cargo doc. Immediately, at the very top of the output, you should see the warning above. (If you don't see the warning, make sure you have the latest Rust compiler by running rustup update)

To fix this, go look at the issue mentioned in the warning and figure out what changes need to be made to Cargo.toml in order for this warning to stop being produced. You'll know you fixed it when you run cargo doc and the warning no longer occurs.

[pickfire]

@sunjay I think this can be closed. It is fixed in #95 by @zachlute.

[sunjay]

You're absolutely right! Thank you!