For local repos, consider mechanisms faster than cloning or copying

[lionel]

This P.R. added the ability to use local repos: Support locally cloned kernel paths #46

It currently does a file copy of the entire repo. It can be especially slow on a large repo with a lot of history, such as the linux kernel. Sooner or later, I or someone else will want something faster.

For example, adding a git worktree is much faster than cloning or copying.