Exporting a nar and importing it on another machine only works when the package being built has a single output.
I set up a signing-key on the sending machine, authorized it on the receiving machine, and successfully transferred some nars of single-output packages. I say they succeeded because `guix build --no-grafts foo` did not need to build foo after having imported the nar archive built on the other machine. However, it fails for packages with multiple outputs such as Syncthing and libsmf. I made sure both sides were trying to build the same derivation by using `guix time-machine` and created the archives like this: $ guix time-machine --commit=03f9a8c35be387f37badcd2c830ac7414ac17225 -- archive -r --no-grafts --export libsmf > ~/tmp/libsmf.nar
