Change TypeScript import to match module definition

index.d.ts

@@ -1,7 +1,7 @@
 import * as http from 'http';
 import * as https from 'http';
 import { Options as BaseRetryOptions } from 'async-retry';
-import { Request, RequestInit, Response } from 'node-fetch';
+import { Headers, Request, RequestInit, Response } from 'node-fetch';
 
 export interface RetryOptions extends BaseRetryOptions {
 	maxRetryAfter?: number;
@@ -17,5 +17,14 @@ export type Fetch = (
 	options?: FetchOptions
 ) => Promise<Response>;
 
-export default function SetupFetch(client?: Fetch, agentOptions?: http.AgentOptions | https.AgentOptions): Fetch;
+export type FetchModule = {
+	default: Fetch;
+	Headers: typeof Headers;
+}
+
+export default function SetupFetch(
+	fetchModule?: FetchModule,
+	agentOptions?: http.AgentOptions | https.AgentOptions
+): Fetch;
+
 export * from 'node-fetch';

readme.md

@@ -20,8 +20,18 @@ if not provided, with the following settings:
 
 ## How to use
 
+JavaScript
+
 ```js
 const fetch = require('@zeit/fetch')(require('some-fetch-implementation'))
 ```
 
+TypeScript
+
+```typescript
+import createFetch from "@zeit/fetch"
+import * as fetch from "some-fetch-implementation";
+const fetch = createFetch(fetch);
+```
+
 If no fetch implementation is supplied, it will attempt to use peerDep `node-fetch`.