Updated CHANGELOG

Signed-off-by: Marco Pracucci <marco@pracucci.com>

CHANGELOG.md

@@ -9,6 +9,12 @@ NOTE: As semantic versioning states all 0.y.z releases can contain breaking chan
 
 We use *breaking* word for marking changes that are not backward compatible (relates only to v0.y.z releases.)
 
+## Unreleased
+
+### Added
+
+- [#2502](https://github.com/thanos-io/thanos/pull/2502) Added `hints_enabled` proto field to `SeriesRequest` and `hints` field to `SeriesResponse`. Hints in an opaque data structure that can be used to carry information about how the series and its content is implementation specific.
+
 ## [v0.12.1](https://github.com/thanos-io/thanos/releases/tag/v0.12.1) - 2020.04.20
 
 ### Fixed
@@ -23,8 +29,6 @@ We use *breaking* word for marking changes that are not backward compatible (rel
 - [#2416](https://github.com/thanos-io/thanos/pull/2416) Bucket: fixes issue #2416 bug in `inspect --sort-by` doesn't work correctly in all cases
 - [#2411](https://github.com/thanos-io/thanos/pull/2411) Query: fix a bug where queries might not time out sometimes due to issues with one or more StoreAPIs
 
-### Added
-
 ### Changed
 - [#2450](https://github.com/thanos-io/thanos/pull/2450) Store: regex-set optimization for `label=~"a|b|c"` matchers.
 - [#2475](https://github.com/thanos-io/thanos/pull/2475) Store: remove incorrect optimizations for queries with `=~".*"` and `!=~".*"` matchers.