code: function addDiffIndicator(str, added) {
      const modifier = added ? '+' : '-';
      if (str[0] === ' ') {
          return modifier + str.slice(1);
      } else {
          return `${modifier}${str}`;
      }
  }
docs: Add the diff indicator to the first character of the input (if it's a space) otherwise prepend it
  @param {String} str - the string to add a diff indicator to
  @param {Boolean} added - true if added, false if removed
  @returns {String} the augmented string