Add link for creating schema file

[kevanstannard]

I'm new to GraphQL and was curious how to create the schema file mentioned in the "2. Set up compiler." section.

Previously I've used send-introspection-query from the graphql_ppx package, but I'm investigating how to achieve the same result without that package.

I found the Apollo Remote schemas documentation. Is this the correct instructions for creating the schema file needed by reasonql?

Would be great if the docs could include a link to more details for creating the schema file for people new to GraphQL.

Thank you