update changelog; clairify test fixture usage

Author: chrisdicaprio

CHANGELOG.md

@@ -1,16 +1,15 @@
 # Changelog
 
-## [2.1.0] Unreleased
+## [2.1.0] 2026-05-15
 ### Added
 - `OqHdf5Reader` to replace OpenQuake `Extractor`
   - Test against hdf5 fixtures generated by range of OpenQuake versions
   - `scripts/regen_oq_fixtures.py` to (re)generate test fixtures
   - `tests/oq_import/test_extractor_compat.py` to test against OpenQuake `Extractor`
   - Documentation
-  - `oq-compat` dependency group. Only used for running `tests/oq_import/test_extractor_compat.py`
 
-### Removed
-- `openquake` optional dependency group
+### Changed
+  - `oq-compat` dependency group used for running `tests/oq_import/test_extractor_compat.py` (used to be `openquake` extra dependency)
 
 ## [2.0.1] 2026-05-11
 ### Added

docs/h5py_extractor_migration.md

@@ -63,7 +63,7 @@ The rlz axis ordering follows `best_rlzs[site_idx]` — an integer array giving
 
 ### Generating fixtures
 
-A developer may want to generate new fixtures when either new functionality is added to `OqHdf5Reader` that reads features not present in the existing fixtures or they want to support new versions of OpenQuake.
+A developer may want to generate new test fixtures when either new functionality is added to `OqHdf5Reader` that reads features not present in the existing fixtures or they want to support new versions of OpenQuake. These fixtures are then used to make sure that `OqHdf5Reader` continues to behave as expected via tests in `tests/oq_import/test_cross_version_fixtures.py` and `tests/oq_import/test_extractor_snapshot_cross_version.py`.
 
 Prerequisites: Docker installed and `openquake/engine:<ver>` images pullable.