doc: added some basic top-level documentation.

src/errors.rs

@@ -5,6 +5,7 @@ use chownr;
 use failure::Fail;
 use serde_json;
 
+/// Error type returned by all API calls.
 #[derive(Fail, Debug)]
 pub enum Error {
     #[fail(display = "not found")]

src/get.rs

@@ -1,3 +1,4 @@
+//! Functions for reading from cache.
 use std::path::Path;
 
 use ssri::Integrity;

src/index.rs

@@ -18,6 +18,7 @@ use crate::errors::Error;
 
 const INDEX_VERSION: &str = "5";
 
+/// Represents a cache index entry, which points to content.
 #[derive(PartialEq, Debug)]
 pub struct Entry {
     pub key: String,

src/lib.rs

@@ -1,3 +1,7 @@
+//! cacache is a Rust library for managing local key and content address
+//! caches. It's really fast, really good at concurrency, and it will never
+//! give you corrupted data, even if cache files get corrupted or manipulated.
+
 mod content;
 pub mod get;
 pub mod put;

src/put.rs

@@ -1,3 +1,4 @@
+//! Functions for writing to cache.
 use std::path::{Path, PathBuf};
 
 use nix::unistd::{Uid, Gid};

src/rm.rs

@@ -1,3 +1,4 @@
+//! Functions for removing things from the cache.
 use std::fs;
 use std::path::Path;