if (window.attachEvent) {
  window.attachEvent('onload', add_source_url);
} else if (window.addEventListener) {
  window.addEventListener('load', add_source_url, false);
}

function add_source_url() {
  var sel_txt = '';
  var src_url = '';
  document.body.oncopy = function() {
    window.event.returnValue = false;
    sel_txt = document.selection.createRange().text;
    src_url = location.href;
    clipboardData.setData('Text', sel_txt + '\r\n' + 'Read More: ' + src_url);
  }
}