code: function addCommand(descriptor){
  	// Check descriptor type.
  	var err = {};
  	if( !checkDescriptor(descriptor, err) ){
  		logger.error(
  			'The command descriptor is invalid.',
  			new Error('[command.io] Invalid command descriptor ("'+err.key+'": expected "'+err.expect+'", have "'+err.type+'").')
  		);
  		logger.error('Please check this doc: https://github.com/Techniv/node-command-io/wiki/Command-descriptor-refactoring');
  		return module.exports;
  	}
  
  	var name = descriptor.name;
  	descriptor.controller = new CommandController(descriptor);
  
      // Index the command descriptor
      commandDescriptors[name] = descriptor;
  
      // Chain addCommand
      return module.exports;
  }
docs: Add a command
  @param name string
  @param description string
  @param action Function
  @returns Object return Command.IO API.