Add a proper description to the README.md and include it in lib.rs

README.md

@@ -1,7 +1,21 @@
 ![](https://github.com/matthewscottgordon/vanrijn/workflows/Rust/badge.svg)
 
-# vanrijn
-Ray tracer
+# Vanrijn
 
-![Rendered test image of three spheres](.github/output.png?raw=true "Test Image")
-![Rendered test image of three spheres and a bunny](.github/output2.png?raw=true "Test Image")
+Vanrijn is a [physically based](https://en.wikipedia.org/wiki/Physically_based_rendering)
+[ray tracer](https://en.wikipedia.org/wiki/Ray_tracing_(graphics)). Many thanks to the
+authors of the book
+["Physically Based Rendering: From Theory to Implementation](https://www.pbrt.org/) from
+which many of the algorithms used here are taken. This is, however _not_ a Rust port of
+the C++ PBRT rederer described in that book.
+
+This crate is structured as a library; main.rs is just a glorified test harness which
+shows an example of using the library to render a scene. It uses SDL2 to display the
+rendered image.
+
+On Ubuntu 19.04, if you have the libsdl2-dev package installed you should be able to
+run "cargo run" and see a window with a test scene rendered into it. In theory it should
+work on any platform with SDL2 installed but I've only tested it on Ubuntu Linux.
+
+![](.github/output.png?raw=true "Test Image 1")
+![](.github/output2.png?raw=true "Test Image")

src/lib.rs

@@ -1,3 +1,6 @@
+#![feature(external_doc)]
+#![doc(include = "../README.md")]
+
 pub mod camera;
 pub mod colour;
 pub mod image;