Set source roots when multiple packages specified

[ckchow]

Poetry itself supports nonstandard project setups where potentially multiple packages are included in one distribution: https://python-poetry.org/docs/pyproject/#packages. Maybe this plugin can use that information to automatically set up sources roots.

[koxudaxi]

@ckchow
Thank you for creating this issue.
I think the feature is for distributing packages.
But, Did you want to use it to set source roots?
It's a great idea 🚀
I will implement it for 1.0 or later.