add github.com/docker/docker dependency

vendor/github.com/docker/distribution/docs/spec/implementations.md

@@ -0,0 +1,30 @@
+---
+published: false
+---
+
+# Distribution API Implementations
+
+This is a list of known implementations of the Distribution API spec.
+
+## [Docker Distribution Registry](https://github.com/docker/distribution)
+
+Docker distribution is the reference implementation of the distribution API
+specification. It aims to fully implement the entire specification.
+
+### Releases
+#### 2.0.1 (_in development_)
+Implements API 2.0.1
+
+_Known Issues_
+ - No resumable push support
+ - Content ranges ignored
+ - Blob upload status will always return a starting range of 0
+
+#### 2.0.0
+Implements API 2.0.0
+
+_Known Issues_
+ - No resumable push support
+ - No PATCH implementation for blob upload
+ - Content ranges ignored
+