Add breaking changes to CHANGES.md

Author: manics

CHANGES.md

@@ -7,6 +7,31 @@ deployed to production at mybinder.org quickly after they are merged
 As such, this changelog is broken up by dates, not versions, and is just to
 make it easier to track what has changed over time_
 
+# 0.2.0...HEAD
+
+([full changelog](https://github.com/jupyterhub/binderhub/compare/0.2.0...HEAD))
+
+## Breaking changes
+
+The `binderhub.build.Build` class is replaced by the Traitlets based `binderhub.build.KubernetesBuildExecutor` class [#1581](https://github.com/jupyterhub/binderhub/pull/1581), [#1521](https://github.com/jupyterhub/binderhub/pull/1521).
+The following build configuration properties should be set using Traitlets in the BinderHub configuration:
+
+- `c.BinderHub.appendix` ➡️ `c.BuildExecutor.appendix`
+- `c.BinderHub.sticky_builds` ➡️ `c.KubernetesBuildExecutor.sticky_builds`
+- `c.BinderHub.log_tail_lines` ➡️ `c.KubernetesBuildExecutor.log_tail_lines`
+- `c.BinderHub.push_secret` ➡️ `c.BuildExecutor.push_secret`
+- `c.BinderHub.build_memory_request` ➡️ `c.KubernetesBuildExecutor.memory_request`
+- `c.BinderHub.build_memory_limit` ➡️ `c.BuildExecutor.memory_limit`
+- `c.BinderHub.build_docker_host` ➡️ `c.KubernetesBuildExecutor.docker_host`
+- `c.BinderHub.build_namespace` ➡️ `c.KubernetesBuildExecutor.namespace`
+- `c.BinderHub.build_image` ➡️ `c.KubernetesBuildExecutor.build_image`
+- `c.BinderHub.build_node_selector` ➡️ `c.KubernetesBuildExecutor.node_selector`
+
+If you have subclassed `binderhub.build.Build` you must update your subclass (including `__init__()` if defined) to inherit from `binderhub.build.KubernetesBuildExecutor`.
+The behaviour of the class is otherwise unchanged.
+
+# 0.2.0
+
 # master@{2019-07-01}...master@{2019-10-01}
 
 ([full changelog](https://github.com/jupyterhub/binderhub/compare/01b1c59b9e7dc81250c1ed579c492ec2fd6baaf6...a168d069772012c52f9ac7056ec22d779927ae69))