Add subscription type docs
Add subscription type docs

xuorig/graphql-ruby,nevesenin/graphql-ruby,nevesenin/graphql-ruby,rmosolgo/graphql-ruby,nevesenin/graphql-ruby,xuorig/graphql-ruby,rmosolgo/graphql-ruby,nevesenin/graphql-ruby,rmosolgo/graphql-ruby,rmosolgo/graphql-ruby,xuorig/graphql-ruby