docs: function copyResources(output, plugin) {
      var logger = output.getLogger();
  
      var options    = output.getOptions();
      var outputRoot = options.get('root');
  
      var state = output.getState();
      var resources = state.getResources();
  
      var pluginRoot      = plugin.getPath();
      var pluginResources = resources.get(plugin.getName());
  
      var assetsFolder = pluginResources.get('assets');
      var assetOutputFolder = path.join(outputRoot, 'gitbook', plugin.getNpmID());
  
      if (!assetsFolder) {
          return Promise();
      }
  
      // Resolve assets folder
      assetsFolder = path.resolve(pluginRoot, assetsFolder);
      if (!fs.existsSync(assetsFolder)) {
          logger.warn.ln('assets folder for plugin "' + plugin.getName() + '" doesn\'t exist');
          return Promise();
      }
  
      logger.debug.ln('copy resources from plugin', assetsFolder);
  
      return fs.copyDir(
          assetsFolder,
          assetOutputFolder,
          {
              deleteFirst: false,
              overwrite: true,
              confirm: true
          }
      );
  }