"$schema", "$id", and "description"

[jnareb]

Shouldn't fully featured JSON Schema file include also the following top-level fields:

• $schema: specifies which draft of the JSON Schema standard the schema adheres to
  
  (e.g. https://json-schema.org/draft/2020-12/schema)
  
• $id: sets a URI for the schema
  
  (e.g. https://github.com/iterative/dvcyaml-schema or https://raw.githubusercontent.com/iterative/dvcyaml-schema/master/schema.json)
  
• description: state the intent of the schema
  
  (e.g. Definition of DVC pipeline, or something like that)
  

Taken from https://json-schema.org/learn/getting-started-step-by-step#create-a-schema-definition

[shcheklein]

I'm not an expert but it looks you are right. Please feel free to create a PR with these changes, @jnareb !