* Add the nu-serde crate
nu-serde is a crate that can be used to turn a value implementing
`serde::Serialize` into a `nu-protocol::Value`. This has the potential to
significantly simplify plugin authorship.
This crate was the previously independent
[serde-nu](https://github.com/lily-mara/serde-nu) but the nushell maintainers
expressed an interest in having it added to the mainline nushell repository.
* fixup! Add the nu-serde crate
