message: Link to age crate changelog from rage crate changelog
diff: # Changelog
  -All notable changes to this project will be documented in this file.
  +All notable changes to the rage CLI tools themselves will be documented in this
  +file. Changes to the [age crate](../age/CHANGELOG.md) also apply to the rage CLI
  +tools, and are not duplicated here.
  The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
  and this project adheres to Rust's notion of
  