Improve demo

[PierreDemailly]

The local demo.js is not practical because the user must clone the repository.

I think we can remove it, here is what we can do instead:

• A StackBlitz live demo example
• A demo package (@topcli/prompts-demo ?), example: npx @inquirer/demo (using npm workspaces)

Note: i also thought about a new flag / command (for instance npx @topcli/prompts --demo) but it would pollute the repo.

[fraxken]

Creating a package just for that seems a bit too much