Separate endpoint for GraphiQL

Hi,
wouldn't it make sense to have separate endpoints for GraphQL and GraphiQL? As per [README](https://github.com/graphql-python/flask-graphql#usage), there should be two endpoints (`/graphql` and `/graphiql`), however only `/graphql` gets exposed. Let's say I would like to publish GraphiQL only to selected group of people (e.g. frontend developers) and protect it by authentication. Having a separate endpoint would make whole thing much easier.