`draft pack-repo update` fails with local pack repositories

[jpetazzo]

How to reproduce:

cd /tmp
mkdir -p local-pack-repo/packs/my-local-pack
helm create local-pack-repo/packs/my-local-pack/charts
draft pack-repo add local-pack-repo/
draft pack-repo update

We get the error message:

Error: cannot get information about pack repo source
Error: exit status 1

Cleaning up:

draft pack-repo remove local-pack-repo
rm -rf /tmp/local-pack-repo

Additional notes: I thought that the pack repo had to be a git repo, so I tried various hacks to make it a git repo with a local remote; but nothing worked (it looks like Draft tries to make up a git repo URL from its path, fails, and reports the error anyway).