No description on schemas (e.g. response body schemas)

[ObjectSchema.tsx](https://github.com/Rebilly/ReDoc/blob/master/src/components/Schema/ObjectSchema.tsx) does not render schema description, even though the OpenAPI spec allows it, including using CommonMark in description:

https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.0.md#schemaObject