Built-in readFile function

[philippta]

A new readFile function should be added to the built-in functions under the flyscrape package.

Use-cases:

• Read starting URLs from file. Rel: #8
• Read proxy list from file.

API definiton:

function readFile(name: string): string

Proposed example:

import { readFile } from "flyscrape";

export const config = {
  proxies: readFile("proxylist.txt").split("\n"),
};