* gnu/services/base.scm (guix-machines-files-installation): Handle
machines being a mixed list of build-machines and lists of
build-machines.
* doc/guix.texi (Base Services): Document it.
Change-Id: Ie404562ca0b564413233c3a624046da831893dc3
Co-authored-by: Ludovic Courtès <ludo@gnu.org>