guix-install.sh: Prompt for configuring substitutes discovery....Also ensure prompt_yes_no always print the message with a trailing space,
which is more pleasing to the eye.
* etc/guix-daemon.conf.in <--discover=no>: New guix-daemon option.
* etc/guix-daemon.service.in: Likewise.
* etc/init.d/guix-daemon.in: Likewise.
* etc/openrc/guix-daemon.in: Likewise.
* etc/guix-install.sh (configure_substitute_discovery): New procedure.
(sys_enable_guix_daemon): Ask the user whether automatic substitute discovery
should be enabled. Set the '--discover' argument accordingly.
(prompt_yes_no): Add a trailing space to the message.
(sys_authorize_build_farms): Remove trailing space from the message argument.
* NEWS (Distribution): Add news.
Maxim Cournoyer
2020-03-11
Add system start-up files for guix-daemon....* etc/init.d/guix-daemon.in: New file.
* nix/local.mk (etc/init.d/guix-daemon): New rule.
(nodist_sysvinitservice_DATA): Add etc/init.d/guix-daemon.in .
(CLEANFILES): Add etc/init.d/guix-daemon .
* .gitignore: Add etc/init.d/guix-daemon .