Downsample: update changelog (#2278)

* Downsample: update changelog

Signed-off-by: Xiang Dai <764524258@qq.com>

* feedback

Signed-off-by: Xiang Dai <764524258@qq.com>

CHANGELOG.md

@@ -21,6 +21,10 @@ We use *breaking* word for marking changes that are not backward compatible (rel
 
 - [#2265](https://github.com/thanos-io/thanos/pull/2265) Compactor: Add `--wait-interval` to specify compaction wait interval between consecutive compact runs when `--wait` enabled.
 
+### Changed
+
+- [#2090](https://github.com/thanos-io/thanos/issues/2090) *breaking* Downsample command: the `downsample` command has moved as the `thanos bucket` sub-command, and cannot be called via `thanos downsample` any more.
+
 ## [v0.11.0](https://github.com/thanos-io/thanos/releases/tag/v0.11.0) - 2020.03.02
 
 ### Fixed