code: function addIgnoreFile(ig, filepath) {
          if (fs.existsSync(filepath)) {
            ig.add(fs.readFileSync(filepath).toString());
          }
          return ig;
      }
docs: add ignore file to node-ignore instance
  @param {object} ig, instance of node-ignore
  @param {string} filepath, file to add to ig
  @returns {array} raw ignore rules