The documentation for Registry has been merged into the general documentation repo. Commit history has been preserved.
The docs for Registry are now here: https://github.com/docker/docker.github.io/tree/master/registry
Note: The definitive ./spec directory directory and configuration.md file will be maintained in this repository and be refreshed periodically in the general documentation repo.
As always, the docs in the general repo remain open-source and we appreciate your feedback and pull requests!