It looks like there is now https://www.npmjs.com/package/graphql-docs
Dynamically generated documentation explorer for GraphQL schemas. It aims to provide a better overview of a schema than GraphiQL, but without querying features.
You can also generate a static documentation file based on a schema file or GraphQL endpoint:
npm install -g graphql-docs
graphql-docs-gen http://GRAPHQL_ENDPOINT documentation.html