Edit changelog

Author: jovenlin0527

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Add `Py::setattr` method. [#2009](https://github.com/PyO3/pyo3/pull/2009)
 - Add `PyCapsule`, exposing the [Capsule API](https://docs.python.org/3/c-api/capsule.html#capsules). [#1980](https://github.com/PyO3/pyo3/pull/1980)
+- `#[pyclass]` now supports fieldless enums. It also provide default implementation for `__repr__`, `__int__`, and `__richcmp__` for enums.
 
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