Document how to import graphql files (`typed-query-document`)

[fregante]

Maybe the solution is hidden behind #1046, but so far I'm not seeing any types with the suggested tsconfig:

		"plugins": [
			{
				"name": "ts-graphql-plugin",
				"schema": "https://docs.github.com/public/schema.docs.graphql",
				"typegen": {
					"addons": [
						"ts-graphql-plugin/addons/typed-query-document"
					]
				}
			}
		]

import listPrsForFileQuery from './list-prs-for-file.gql';
// ^ Error: Cannot find module './list-prs-for-file.gql' or its corresponding type declarations.ts(2307)

Until now I had a simple string type export in my globals.d.ts:

declare module '*.gql' {
	export = string;
}

but I suppose I should let the typed query document take over instead, so I removed that declaration.