promise-based init about browserfs

[james-pre]

@konsumer Thanks for opening an issue! I already added this so you should be able to use it like so:

import { configure, BFSRequire } from 'browserfs'
import { Buffer } from 'buffer';

await configure({
  fs: 'OverlayFS',
  options: {
    readable: {
      fs: 'ZipFS',
      options: {
        zipData: Buffer.from(await fetch('myzip.zip').then(r => r.arrayBuffer()))
      }
    },
    writable: {
      fs: 'LocalStorage'
    }
  }
});

const fs = BFSRequire('fs');

Please read Releases and compatibility going forward.