Add entry to changelog

[skip CI]

Author: mulimoen

CHANGELOG.md

@@ -49,6 +49,7 @@
   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 creating external links on a `Group` with `link_external`.
+- Additional iterators for getting groups, datasets, and datatypes.
 
  ### Changed