code: function fromString (string) {
    assert.equal(typeof string, 'string')
  
    return from(function (size, next) {
      if (string.length <= 0) return this.push(null)
  
      const chunk = string.slice(0, size)
      string = string.slice(size)
  
      next(null, chunk)
    })
  }
docs: create a stream from a string str -> stream