Add a note about availability

Author: lornajane

registry/tag-kind.md

@@ -7,6 +7,10 @@ parent: Registry
 
 # Tag Kinds Registry
 
+## Unreleased feature
+
+The `kind` addition to OpenAPI tags is planned for release in OpenAPI 3.2, so support for the values here should not be expected until tools officially support the 3.2 version.
+
 ## Contributing
 
 Please raise a [Pull-Request](https://github.com/OAI/OpenAPI-Specification/pulls) or [Issue](https://github.com/OAI/OpenAPI-Specification/issues) to contribute or discuss a registry value.