Limited license selection in `nimble init`
When running `nimble init`, it asks the user to choose a license. It currently [only supports a very small selection of licenses](https://github.com/nim-lang/nimble/blob/7e3058657c4ff3ca70288595fc2a21f791c50f7c/src/nimble.nim#L770):

- MIT
- BSD 2 Clause
- GPL v3
- LGPL v3
- Apache 2

I noticed this as I usually choose a BSD 3 Clause license for my projects. There should be an option to either specify a custom license, or this list should be expanded upon (I would vote for the first option).