[Feature/Improvement] Allow git repo in parent directory

[romainreignier]

Hi, thank you for this new crate that is quite interesting.

Is your feature request related to a problem? Please describe.
My Rust project is in a sub-directory of a Git repo (embedded project with host tools and shared crates).
I don't use a Cargo workspace otherwise, I can't make rust-analyzer works between the different targets.
So the workspace_root returned by cargo metadata is not a git repo and Repository::open() returns an error (could not find repository at).

Describe the solution you'd like
It would be nice to look for Git repositories in the parent directories (maybe with a limit on the depth).

Describe alternatives you've considered
I guess that using Cargo workspaces would solve the issue but as explained before, I cannot use it in my use case (seems common on embedded projects, example found on Github, not related to me).

[petekubiak]

Thanks for the feedback! I'll see what I can do to support this :)