debhelper add-on to handle runit runscripts

 dh-runit provides a debhelper sequence addon named 'runit' and the
 dh_runit command.
 .
 The dh_runit command installs runscripts and adds the appropriate code to
 the postinst, prerm and postrm maint scripts to properly enable/disable
 and purge runscripts. When runit is PID 1 the maint script code also takes
 care of restarting services during upgrades, when appropriate.