Add clarifaction for WASM usecase

Signed-off-by: James Sturtevant <jstur@microsoft.com>

artifacts-guidance.md

@@ -1,6 +1,6 @@
 # Guidance for Artifacts Authors
 
 Content other than OCI container images MAY be packaged using the image manifest.
-When this is done, the `config.mediaType` value should not be a known OCI image config [media type](media-types.md).
-Historically, due to registry limitations, some tools have created non-OCI conformant artifacts using the `application/vnd.oci.image.config.v1+json` value for `config.mediaType` and values specific to the artifact in `layer[*].mediaType`.
+When this is done, the `config.mediaType` value MAY not be a known OCI image config [media type](media-types.md).
+Historically, due to registry limitations, some tools have created non-OCI conformant artifacts using the `application/vnd.oci.image.config.v1+json` value for `config.mediaType` and values specific to the artifact in `layer[*].mediaType`.  In some cases, the `application/vnd.oci.image.config.v1+json` may still be appropriate if the artifact is to be run via a runtime.
 Implementation details and examples are provided in the [image manifest specification](manifest.md#guidelines-for-artifact-usage).

manifest.md

@@ -255,6 +255,8 @@ The decision tree below and the associated examples MAY be used to design new ar
    }
    ```
 
+   In the case where the artifact may be run by a runtime the `config.mediaType` MAY be `application/vnd.oci.image.config.v1+json`.
+
 _Implementers note:_ artifacts have historically been created without an `artifactType` field, and tooling to work with artifacts should fallback to the `config.mediaType` value.
 
 [iana]:         https://www.iana.org/assignments/media-types/media-types.xhtml