message: Add changelog entry for JSON inspectors
diff: @@ -5,6 +5,11 @@ is based on [Keep a Changelog](https://keepachangelog.com).
  ## [Unreleased]
  +### Added
  +
  +- CAF includes two new inspector types for consuming and generating
  + JSON-formatted text: `json_writer` and `json_reader`.
  +
  ### Changed
  - Setter functions for fields may now return either `bool`, `caf::error` or
  