add breaking changes note to v4 changes

CHANGELOG.md

@@ -15,7 +15,9 @@ upcoming release can be found in [changelog.d](changelog.d).
 ### Changed
 
 - CLI `b2` executable now points to the latest stable ApiVer version, `b2v4`, previously it pointed to `b2v3`.
-  See ApiVer section in the documentation for more details.
+  These means following breaking changes:
+  - `b2` will no longer persists credentials and other secrets on disk if credentials were passed through `B2_*` environment variables. To explicitly persist them and keep using local cache for better performance, user can simply call `b2 account account`
+  - `b2 ls` and `b2 rm` no longer accept two positional arguments, instead accepting only `B2 URI` (e.g. `b2://bucketName/path`)
 - Changed `sync` command exit status code from 0 to 1 if any warnings or errors were encountered during the operation.
 
 ### Fixed