Add glide.yaml and vendor deps

vendor/github.com/opencontainers/image-spec/spec.md

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+# Open Container Initiative Image Format Specification
+
+This specification defines an OCI Image, consisting of a [manifest](manifest.md), a set of [filesystem layers](layer.md), and a [configuration](config.md).
+
+The goal of this specification is to enable the creation of interoperable tools for building, transporting, and preparing a container image to run.
+
+## Table of Contents
+
+- [Introduction](spec.md)
+- [Notational Conventions](#notational-conventions)
+- [Overview](#overview)
+    - [Understanding the Specification](#understanding-the-specification)
+    - [Media Types](media-types.md)
+- [Content Descriptors](descriptor.md)
+- [Image Layout](image-layout.md)
+- [Image Manifest](manifest.md)
+- [Image Manifest List](manifest-list.md)
+- [Filesystem Layers](layer.md)
+- [Image Configuration](config.md)
+- [Canonicalization](canonicalization.md)
+
+# Notational Conventions
+
+The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in [RFC 2119](http://tools.ietf.org/html/rfc2119) (Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997).
+
+The key words "unspecified", "undefined", and "implementation-defined" are to be interpreted as described in the [rationale for the C99 standard][c99-unspecified].
+
+# Overview
+
+At a high level the image manifest contains metadata about the contents and dependencies of the image including the content-addressable identity of one or more [filesystem layer changeset](layer.md) archives that will be unpacked to make up the final runnable filesystem.
+The image configuration includes information such as application arguments, environments, etc.
+
+![](img/build-diagram.png)
+
+Once built the OCI Image can then be discovered by name, downloaded, verified by hash, trusted through a signature, and unpacked into an [OCI Runtime Bundle](https://github.com/opencontainers/runtime-spec/blob/master/bundle.md).
+
+![](img/run-diagram.png)
+
+## Understanding the Specification
+
+The [OCI Image Media Types](media-types.md) document is a starting point to understanding the overall structure of the specification.
+
+The high-level components of the spec include:
+
+* An archival format for container images, consisting of an [image manifest](manifest.md), an [image layout](image-layout.md), a set of [filesystem layers](layer.md), and [image configuration](config.md) (base OCI layer)
+* A [process of referencing container images by a cryptographic hash of their content](descriptor.md) (base OCI layer)
+* A format for [storing CAS blobs and references to them](image-layout.md) (optional OCI layer)
+* Signatures that are based on signing image content address (optional OCI layer)
+* Naming that is federated based on DNS and can be delegated (optional OCI layer)
+
+[c99-unspecified]: http://www.open-std.org/jtc1/sc22/wg14/www/C99RationaleV5.10.pdf#page=18