update changelog (cosmos#83)

* update changelog

* Update CHANGELOG.md

Co-authored-by: Federico Kunze <31522760+fedekunze@users.noreply.github.com>

* Update CHANGELOG.md

Co-authored-by: Federico Kunze <31522760+fedekunze@users.noreply.github.com>

Co-authored-by: Federico Kunze <31522760+fedekunze@users.noreply.github.com>

CHANGELOG.md

@@ -35,3 +35,20 @@ Ref: https://keepachangelog.com/en/1.0.0/
 # Changelog
 
 ## [Unreleased]
+
+### State Machine Breaking
+
+* (modules/core/02-client) [\#8405](https://github.com/cosmos/cosmos-sdk/pull/8405) Refactor IBC client update governance proposals to use a substitute client to update a frozen or expired client.
+* (modules/core/02-client) [\#8673](https://github.com/cosmos/cosmos-sdk/pull/8673) IBC upgrade logic moved to 02-client and an IBC UpgradeProposal is added.
+
+### Improvements
+
+* (modules/core/04-channel) [\#7949](https://github.com/cosmos/cosmos-sdk/issues/7949) Standardized channel `Acknowledgement` moved to its own file. Codec registration redundancy removed.
+
+## IBC in the Cosmos SDK Repository
+
+The IBC module was originally released in [v0.40.0](https://github.com/cosmos/cosmos-sdk/releases/tag/v0.40.0) of the SDK.
+Please see the [Release Notes](https://github.com/cosmos/cosmos-sdk/blob/v0.40.0/RELEASE_NOTES.md).
+
+The IBC module is also contained in the releases for [v0.41.x](https://github.com/cosmos/cosmos-sdk/releases/tag/v0.41.0) and [v0.42.x](https://github.com/cosmos/cosmos-sdk/releases/tag/v0.42.0).
+Please see the Release Notes for [v0.41.x](https://github.com/cosmos/cosmos-sdk/blob/release/v0.41.x/RELEASE_NOTES.md) and [v0.42.x](https://github.com/cosmos/cosmos-sdk/blob/release/v0.42.x/RELEASE_NOTES.md).