Add doc page for breaking changes

Signed-off-by: Arnaud Porterie <arnaud.porterie@docker.com>

docs/breaking_changes.md

@@ -0,0 +1,51 @@
+<!--[metadata]>
++++
+aliases = ["/engine/misc/breaking/"]
+title = "Breaking changes"
+description = "Breaking changes"
+keywords = ["docker, documentation, about, technology, breaking",
+"incompatibilities"]
+[menu.main]
+parent = "engine_use"
+weight=80
++++
+<![end-metadata]-->
+
+# Breaking changes and incompatibilities
+
+Every Engine release strives to be backward compatible with its predecessors.
+In all cases, the policy is that feature removal is communicated two releases
+in advance and documented as part of the [deprecated features](deprecated.md)
+page.
+
+Unfortunately, Docker is a fast moving project, and newly introduced features
+may sometime introduce breaking changes and/or incompatibilities. This page
+documents these by Engine version.
+
+# Engine 1.10
+
+There were two breaking changes in the 1.10 release.
+
+## Registry
+
+Registry 2.3 includes improvements to the image manifest that have caused a
+breaking change. Images pushed by Engine 1.10 to a Registry 2.3 cannot be
+pulled by digest by older Engine versions. A `docker pull` that encounters this
+situation returns the following error:
+
+``` Error response from daemon: unsupported schema version 2 for tag TAGNAME
+```
+
+Docker Content Trust heavily relies on pull by digest. As a result, images
+pushed from the Engine 1.10 CLI to a 2.3 Registry cannot be pulled by older
+Engine CLIs (< 1.10) with Docker Content Trust enabled.
+
+If you are using an older Registry version (< 2.3), this problem does not occur
+with any version of the Engine CLI; push, pull, with and without content trust
+work as you would expect.
+
+## Docker Content Trust
+
+Engine older than the current 1.10 cannot pull images from repositories that
+have enabled key delegation. Key delegation is an experimental feature which
+requires a manual action to enable.