Add Cargo.lock

[jonringer]

I think the rust-lang book was misinterpreted. For applications, it is considered best practice to check in a Cargo.lock

https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html

If you’re building an end product, which are executable like command-line tool or an application, or a system library with crate-type of staticlib or cdylib, check Cargo.lock into git

[dvogt23]

thanks but will fixing that with #22