Add documentation to datafusion-substrait crate about what it does #8820
Description
Is your feature request related to a problem or challenge?
The documentation for the datafusion-substrait crate is pretty much non existent which makes it hard for users to know what it does and how to use it
https://docs.rs/datafusion-substrait/latest/datafusion_substrait/#
Describe the solution you'd like
I would like documentation like datafusion-proto that gives an example and describes what datafusion substrait can be used for
https://docs.rs/crate/datafusion-proto/latest
Describe alternatives you've considered
No response
Additional context
No response