* gnu/services/guix.scm (guix-build-coordinator-configuration-parallel-hooks):
New procedure.
(make-guix-build-coordinator-start-script): Accept and use #:parallel-hooks.
(guix-build-coordinator-shepherd-services): Pass parallel-hooks to
make-guix-build-coordinator-start-script.
* doc/guix.texi (Guix Build Coordinator): Document this new field.