Fix label schema link

This fixes the label schema link since the project is now archived and
certificates are unlikely to be fixed. It also adjusts some markdown
syntax with links at the end and whitespace after headers.

Signed-off-by: Brandon Mitchell <git@bmitch.net>

annotations.md

@@ -1,4 +1,5 @@
 # Annotations
+
 Several components of the specification, like [Image Manifests](manifest.md) and [Descriptors](descriptor.md), feature an optional annotations property, whose format is common and defined in this section.
 
 This property contains arbitrary metadata.
@@ -45,15 +46,15 @@ This specification defines the following annotation keys, intended for but not l
   * This SHOULD be the immediate image sharing zero-indexed layers with the image, such as from a Dockerfile `FROM` statement.
   * This SHOULD NOT reference any other images used to generate the contents of the image (e.g., multi-stage Dockerfile builds).
 * **org.opencontainers.image.base.name** Image reference of the image this image is based on (string)
-  * This SHOULD be image references in the format defined by [distribution/distribution](https://github.com/distribution/distribution/blob/d0deff9cd6c2b8c82c6f3d1c713af51df099d07b/reference/reference.go).
+  * This SHOULD be image references in the format defined by [distribution/distribution][distribution-reference].
   * This SHOULD be a fully qualified reference name, without any assumed default registry. (e.g., `registry.example.com/my-org/my-image:tag` instead of `my-org/my-image:tag`).
   * This SHOULD be the immediate image sharing zero-indexed layers with the image, such as from a Dockerfile `FROM` statement.
   * This SHOULD NOT reference any other images used to generate the contents of the image (e.g., multi-stage Dockerfile builds).
   * If the `image.base.name` annotation is specified, the `image.base.digest` annotation SHOULD be the digest of the manifest referenced by the `image.ref.name` annotation.
 
 ## Back-compatibility with Label Schema
 
-[Label Schema](https://label-schema.org) defined a number of conventional labels for container images, and these are now superceded by annotations with keys starting **org.opencontainers.image**.
+[Label Schema][label-schema] defined a number of conventional labels for container images, and these are now superceded by annotations with keys starting **org.opencontainers.image**.
 
 While users are encouraged to use the **org.opencontainers.image** keys, tools MAY choose to support compatible annotations using the **org.label-schema** prefix as follows.
 
@@ -74,6 +75,7 @@ While users are encouraged to use the **org.opencontainers.image** keys, tools M
 | | `schema-version`| No equivalent in the OCI Image Spec |
 | | `docker.*`, `rkt.*` | No equivalent in the OCI Image Spec |
 
-[spdx-license-expression]: https://spdx.org/spdx-specification-21-web-version#h.jxpfx0ykyb60
-
+[distribution-reference]: https://github.com/distribution/distribution/blob/d0deff9cd6c2b8c82c6f3d1c713af51df099d07b/reference/reference.go
+[label-schema]: https://github.com/label-schema/label-schema.org/blob/gh-pages/rc1.md
 [rfc3339]:     https://tools.ietf.org/html/rfc3339#section-5.6
+[spdx-license-expression]: https://spdx.org/spdx-specification-21-web-version#h.jxpfx0ykyb60