code: function setup (cb) {
    // the address we are sending from
    var publicKeyBuf = Buffer.from(keyPair.publicKey, 'hex')
    var address = utils.pubToAddress(publicKeyBuf, true)
  
    // create a new account
    var account = new Account()
  
    // give the account some wei.
    //    Note: this needs to be a `Buffer` or a string. All
    //      strings need to be in hex.
    account.balance = '0xf00000000000000001'
  
    // store in the trie
    stateTrie.put(address, account.serialize(), cb)
  }
docs: sets up the initial state and runs the callback when complete