Clones your own config repository (git@host:owner/repo, https://...,
github:owner/repo) into ~/nix-config or --dir and installs it like
--flake <dir>. An existing clone of the same repository (any URL form) is
reused and, after asking, pulled with --ff-only; another repository, a
non-clone or a different branch is refused. A failed clone hints at SSH
URLs and gh auth login. Uses SteamOS' git, else Nix's.
Checked against local bare repositories through a logging git.
Pierre Kisters
da01b7e5ac