Mention the format registry in the data types section

Author: handrews

versions/3.0.4.md

@@ -182,6 +182,8 @@ Models are defined using the [Schema Object](#schemaObject), which is an extende
 OAS uses several known formats to define in fine detail the data type being used.
 However, to support documentation needs, the `format` property is an open `string`-valued property, and can have any value.
 Formats such as `"email"`, `"uuid"`, and so on, MAY be used even though they are not defined by this specification.
+The OpenAPI Initiative also hosts a [Format Registry](https://spec.openapis.org/registry/format/) for formats defined by OAS users and other specifications.  Support for any registry format is strictly OPTIONAL, and support for one registry format does not imply support for any others.
+
 Types that are not accompanied by a `format` property follow the type definition in the JSON Schema. Tools that do not recognize a specific `format` MAY default back to the `type` alone, as if the `format` is not specified.
 
 The formats defined by the OAS are: