create form component using sightly

If you are using AEM 6  and want to use forms - why not use Adaptive Forms? 

https://helpx.adobe.com/aem-forms/6/introduction-forms-authoring.html

You can use Adative Forms and post to an OSGi service - then you can process the form data to meet your business requirements:

https://helpx.adobe.com/experience-manager/using/posting-aem-6-form-data.html

Its much better to use Adaptive forms in AEM 6 then trying to create a form component using Sightly.