One issue with cargoSha256 is that it's hard to detect when it needs to
be updated or not. It's possible to upgrade a package and forget to
update cargoSha256 and run with old versions of the program or
libraries.
This commit introduces `verifyCargoDeps` which, when enabled, will check
that the Cargo.lock is not out of date in the cargoDeps by comparing it
with the package source.
- Add example for setting up nix-shell, improve rust docs
- Rust docs: add gcc rust dependencies and fix carnix commands
- Fix a typo with the carnix command.
