Enhancement: add the watch script from react nodegui

[bradmartin]

Searched for awhile to find a way to reload changes during development and stumbled on https://github.com/nodegui/react-nodegui/issues/5 with the script.

To do: Add the devDep of nodemon and the start:watch script to the template with docs mentioning it, but likely it should be the default for start as most devs assume things are going to be synced/reloaded in some manner on changes.

I'd be glad to provide the PR for this. Let me know if this is something you all would like to see happen to improve the starting experience for NodeGUI 😄