Feature request: detect the repo root

[Offirmo]

First thanks for this useful tool.

My monorepo is not in the git repo's root but in a subfolder. When I launch manypkg, it complains about the "repository field" but incorrectly generates them because it is not taking the subfolder into account.

Ex. manypgk generates

https://github.com/Offirmo/offirmo-monorepo/tree/main/2-foundation/prettify-any

When it should be:

https://github.com/Offirmo/offirmo-monorepo/tree/main/stack--2022/2-foundation/prettify-any

Could we have a proper detection of the repo root?

I'll understand if this case is evaluated as too rare.