message: Clarify changelog
diff: only supports the same operations as `hdf5` (e.g. one can not perform partial IO,
  but must read the entire attribute at once).
  - Added support in `hdf5-sys` for the new functions in `hdf5` `1.10.6` and `1.10.7`.
  -- Added support for external links. New method for `Group`: `link_external`.
  +- Added support for creating external links on a `Group` with `link_external`.
  ### Changed
  