Add some documentation for mesh module

src/lib.rs

@@ -6,6 +6,7 @@ pub mod colour;
 pub mod image;
 pub mod integrators;
 pub mod materials;
+/// Import triangle meshes from model files such as .obj
 pub mod mesh;
 /// Core raycasting and geometry primitives
 pub mod raycasting;

src/mesh.rs

@@ -1,3 +1,4 @@
+/// Load a model from a Wavefront .obj file
 mod wavefront_obj {
     use crate::materials::Material;
     use crate::Real;