add crypto docs.
#![cfg_attr(feature = "cargo-clippy", allow(clippy::reversed_empty_ranges))]
+
+/// This crate implements five different cryptographically secure cipher algorithms:
+/// - Poly1305
+/// - ChaCha20
+/// - XChaCha20
+/// - ChaCha20-Poly1305
+/// - XChaCha20-Poly1305
+///
+/// The internals of these algorithms are defined using macros to make them compose with one another.
+///
use thiserror::Error as DeriveError;
#[macro_use]
