Usually you would want to use git fetch, which is a
higher level wrapper of this command, instead.
Invokes git-upload-pack on a possibly remote repository
and asks it to send objects missing from this repository, to
update the named heads. The list of commits available locally
is found out by scanning the local refs/ hierarchy and sent to
git-upload-pack running on the other end.
This command degenerates to download everything to complete the
asked refs from the remote side when the local side does not
have a common ancestor commit.