This is a simple approach for setting up a mirroring repository.
It will work with any type of remotes.
Mirror --from is more expensive than mirror --to in general.
OTOH, mirror --from will get the file from any remote that has it, not only
the named mirror remote. And if the named mirror remote is not the fastest
available remote with a file, that can speed things up.
It would be possible to make the assistant or watch command do a more
dynamic mirroring, that didn't need to scan every time.
