Begin adding some documentation.

README.md

@@ -0,0 +1,10 @@
+`rustructure` supports walking over designated Rust types at run-time.
+
+This allows for some level of introspection from the perspective of libraries
+that consume external types that can be prepared for their consumption. One
+motivating example is when generating code for serialization or
+deserialization as a complement to `serde` when a format requires foreknowledge
+of the type at a time it is impossible to have an actual instance of the type.
+
+This crate _can_ be `no_std` by removing the default `std` feature, though
+without `alloc` its usefulness is likely limited.

rustructure/src/lib.rs

@@ -1,9 +1,12 @@
+#![doc = include_str!("../../README.md")]
+
 #![cfg_attr(not(feature = "std"), no_std)]
 
 pub use rustructure_macros::Walkable;
 
 mod impls;
 
+/// For `Walker::visit_integer`, the type of integer encountered.
 #[allow(non_camel_case_types)]
 pub enum IntegerType {
     u8,
@@ -17,6 +20,10 @@ pub enum IntegerType {
     usize,
 }
 
+/// User-facing type.
+///
+/// In the non-leaf functions (those that take a `Walkable` generic), if recursion
+/// should take place, it can be invoked at a place of your choosing via `W::walk_with(self)`.
 pub trait Walker {
     fn visit_unit(&mut self);
     fn visit_integer(&mut self, itype: IntegerType);