Document schema that uses graphql modules

Right now you can't document a file that uses graphql modules (via a package like `graphql-import`). If this was added is this something that would be useful to most users? It would be a simple case of running the `graphql-import` function on the schema before it is build in the idl.ts loader. More than happy to submit a PR for this or am I better off forking and doing this for my own use?