message: age: Add async feature flag to changelog
diff: @@ -10,7 +10,8 @@ to 1.0.0 are beta releases.
  ## [Unreleased]
  ### Added
  -- Asynchronous APIs for encryption and decryption:
  +- Asynchronous APIs for encryption and decryption, enabled by the `async`
  + feature flag:
  - `age::Encryptor::wrap_async_output()`
  - `age::Decryptor::new_async()`
  - `age::decryptor::RecipientsDecryptor::decrypt_async()`
  