Settle on "Workflows Description" rather than "document" - similar to OpenAPI developments

[frankkilcommins]

OpenAPI Description is being settled on as a way to refer to a document (or set of documents) that described an API conforming to the OpenAPI Specification. This issue is to apply similar nomenclature within the Workflows Specification.

For reference see:

• Settle on "OpenAPI Description" (3.0.4) OpenAPI-Specification#3384
• Settle on "OpenAPI Description" (3.1.1) OpenAPI-Specification#3385
• Standardize on "Description" as discussed on Slack learn.openapis.org#66