Better documentation for building for Rust

[EatonWu]

This might just be a me issue, but I'm having a hell of a time understanding the requirements for successfully building Perspective for Rust and getting the examples to successfully compile.

I think it would be incredibly helpful to improve the docs.rs documentation.

Within the rust directory, there are perspective-js, and perspective-python directories; why? Are they part of the build process?

Looking at the rust-axum example, it looks like it imports the entire perspective crate directly. There also appears to be a Yew component module, which was my initial use case; however, there's also a perspective-viewer custom element? What are we supposed to actually use?

There seem to be metadata and bundle rust programs that are part of the build process that (I think) aren't mentioned anywhere.

Looking at the github workflow, pnpm is what's used for building for Windows?
Looks like running pip install on the python directory is also a requirement?

Thanks for any help. I'd be happy to update the documentation if I figure anything concrete out.