code: func ReadConfigFile(cliConfigPath string) (*FileConfig, error) {
  	configFilePath := defaults.ConfigFilePath
  	// --config tells us to use a specific conf. file:
  	if cliConfigPath != "" {
  		configFilePath = cliConfigPath
  		if !fileExists(configFilePath) {
  			return nil, trace.Errorf("file not found: %s", configFilePath)
  		}
  	}
  	// default config doesn't exist? quietly return:
  	if !fileExists(configFilePath) {
  		log.Info("not using a config file")
  		return nil, nil
  	}
  	log.Debug("reading config file: ", configFilePath)
  	return ReadFromFile(configFilePath)
  }
docs: // readConfigFile reads /etc/teleport.yaml (or whatever is passed via --config flag)
  // and overrides values in 'cfg' structure