Unpublished Modules will not appear inside the Module Store and, as such, you cannot add them to your Dashboards the conventional way.
First, make sure you have a Dashboard ready. It is recommended to have a Dashboard made purely for Development purposes. Once ready, follow these instructions:
And there you go, your unpublished Module is now on your Dashboard ready to develop!
Now that your scaffolded Module is on a Dashboard, you can start actual development on it!