update changelog to cover MRF describe API.

CHANGELOG.md

@@ -44,6 +44,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - MRF: ensure that subdomain_match calls are case-insensitive
 
 ### Added
+- **Breaking:** MRF describe API, which adds support for exposing configuration information about MRF policies to NodeInfo.
+  Custom modules will need to be updated by adding, at the very least, `def describe, do: {:ok, %{}}` to the MRF policy modules.
 - MRF: Support for priming the mediaproxy cache (`Pleroma.Web.ActivityPub.MRF.MediaProxyWarmingPolicy`)
 - MRF: Support for excluding specific domains from Transparency.
 - MRF: Support for filtering posts based on who they mention (`Pleroma.Web.ActivityPub.MRF.MentionPolicy`)