Check in Cargo.lock

[legendofmiracles]

This helps with reproducibility, and is also the recommended way for rust programs.
The .gitignore says it ignores it, because this program is a library, which just isn't true.

It would also stop distro maintainers from having to patch in the Cargo.lock, as seen here: https://github.com/NixOS/nixpkgs/pull/124539/files

Thanks!

[facundoolano]

@legendofmiracles Thanks for reporting.

When it's available, I would appreciate if you send a PR with instructions to install with nix in the README.