Add changelog entry for FDS reader

Add a changelog entry about the FDS reader being able to read cell-centered data.

Documentation/release/dev/fix-slice-and-boundary-data-in-fds-reader.md

+## Fix slice and boundary data in FDS reader
+
+The FDS reader now correctly supports reading slice & boundaries files (.sf & .bf),
+for both point & cell-centered data. Before these changes, only point data for slices
+was correctly parsed and tested.