message: Improve error message when unable to initialize git index repo
  With this - it'll be more obvious which git repo
  couldn't be initialized.
diff: @@ -88,8 +88,9 @@ impl<'cfg> RemoteRegistry<'cfg> {
  // things that we don't want.
  let mut opts = git2::RepositoryInitOptions::new();
  opts.external_template(false);
  - Ok(git2::Repository::init_opts(&path, &opts)
  - .with_context(|| "failed to initialize index git repository")?)
  + Ok(git2::Repository::init_opts(&path, &opts).with_context(|| {
  + format!("failed to initialize index git repository (in {:?})", path)
  + })?)
  }
  }
  })
  