Mostrar Formulario

 function mostrarFormulario() {

  var html = HtmlService.createTemplateFromFile('Index.html').evaluate()

    .setTitle('Acceso')

    .setWidth(450)

    .setHeight(500);

  SpreadsheetApp.getUi().showModelessDialog(html, 'Formulario Contrata');

}

function onOpen() {

  SpreadsheetApp.getUi().createMenu('Contrata')

    .addItem('Formulario Contrata', 'mostrarFormulario')

    .addToUi();

}