Merge pull request #35149 from AkihiroSuda/image-v1

image/spec: add historical information about v1 spec

image/spec/README.md

@@ -0,0 +1,46 @@
+# Docker Image Specification v1.
+
+This directory contains documents about Docker Image Specification v1.X.
+
+The v1 file layout and manifests are no longer used in Moby and Docker, except in `docker save` and `docker load`.
+
+However, v1 Image JSON (`application/vnd.docker.container.image.v1+json`) has been still widely
+used and officially adopted in [V2 manifest](https://github.com/docker/distribution/blob/master/docs/spec/manifest-v2-2.md)
+and in [OCI Image Format Specification](https://github.com/opencontainers/image-spec).
+
+## v1.X rough Changelog
+
+All 1.X versions are compatible with older ones.
+
+### [v1.2](v1.2.md)
+
+* Implemented in Docker v1.12 (July, 2016)
+* The official spec document was written in August 2016 ([#25750](https://github.com/moby/moby/pull/25750))
+
+Changes:
+
+* `Healthcheck` struct was added to Image JSON
+
+### [v1.1](v1.1.md)
+
+* Implemented in Docker v1.10 (February, 2016)
+* The official spec document was written in April 2016 ([#22264](https://github.com/moby/moby/pull/22264))
+
+Changes:
+
+* IDs were made into SHA256 digest values rather than random values
+* Layer directory names were made into deterministic values rather than random ID values
+* `manifest.json` was added 
+
+### [v1](v1.md)
+
+* The initial revision
+* The official spec document was written in late 2014 ([#9560](https://github.com/moby/moby/pull/9560)), but actual implementations had existed even earlier
+
+
+## Related specifications
+
+* [Open Containers Initiative (OCI) Image Format Specification v1.0.0](https://github.com/opencontainers/image-spec/tree/v1.0.0)
+* [Docker Image Manifest Version 2, Schema 2](https://github.com/docker/distribution/blob/master/docs/spec/manifest-v2-2.md)
+* [Docker Image Manifest Version 2, Schema 1](https://github.com/docker/distribution/blob/master/docs/spec/manifest-v2-1.md) (*DEPRECATED*)
+* [Docker Registry HTTP API V2](https://docs.docker.com/registry/spec/api/)