Write Library Documentation

[mstallmo]

We're going to need some good documentation for library examples and usage that will be published on docs.rs once we publish the crate to crates.io. We will also need to fill out the README so that people coming to the project have some background info and an explanation of what the project does.

List of things to document:
TensorRT

• lib.rs
• engine.rs
• dims.rs
• uff.rs
• builder.rs
• context.rs
• network.rs
• runtime.rs