code: func (c *cmd) readConfig() *config.RuntimeConfig {
  	b, err := config.NewBuilder(c.flagArgs)
  	if err != nil {
  		c.UI.Error(err.Error())
  		return nil
  	}
  	cfg, err := b.BuildAndValidate()
  	if err != nil {
  		c.UI.Error(err.Error())
  		return nil
  	}
  	for _, w := range b.Warnings {
  		c.UI.Warn(w)
  	}
  	return &cfg
  }
docs: // readConfig is responsible for setup of our configuration using
  // the command line and any file configs