AddQuotesPlugin.gs

/**
 * Adds a custom menu with items to show the sidebar and dialog.
 *
 * @param {Object} e The event parameter for a simple onOpen trigger.
 */
function onOpen(e) {
  SpreadsheetApp.getUi()
      .createAddonMenu()
      .addItem('Add Quotes', 'addQuotes')
      .addToUi();
}

/**
 * Runs when the add-on is installed; calls onOpen() to ensure menu creation and
 * any other initializion work is done immediately.
 *
 * @param {Object} e The event parameter for a simple onInstall trigger.
 */
function onInstall(e) {
  onOpen(e);
}

function addQuotes() {
  var range = SpreadsheetApp.getActiveSheet().getActiveRange();
  var values = range.getValues();
  for (var i = 0;i<values.length;i++) {
    values[i][0] = "'"+values[i][0];
  }  
  range.setValues(values);
}