Expanded docs for simple_rng

[joshfactorial]

Is your feature request related to a problem? Please describe.
I haven't fully explored the documentation side of Rust, so some of that is lacking throughout, other than line comments. Expanding the documentation of this section might provide a solid template for the rest.

Describe the solution you'd like
Starting with what they have in the Rust book: https://doc.rust-lang.org/book/ch14-02-publishing-to-crates-io.html?highlight=Documentation#making-useful-documentation-comments

• Review rust docs for Documentation recommended practices
• Review existing comments in simple_rng/src/lib.rs
• Update, request clarification, expand as needed