Add documentation

[bvssvni]

There is little documentation in the library...

[Cifram]

Do you consider the recent update to README.md sufficient?

[brendanzab]

I think we need to move the README docs into doc comments

[Cifram]

I think adding the doc comments would be useful, but not as a replacement for the README. The doc comments are great for explaining a thing once you're looking at it, but the README gives the overview of what to look at.

That said, I think the README could still be a good deal better organized. We could potentially remove most of the function signatures from the README and replace them with links to rust-doc. Then the README would just serve as a quick reference for what types of noise functions are available.

[brendanzab]

Yeah, I think the README might be better if it had a high level overview with a simple example.

[David-OConnor]

*delete