add s6 and runit scripts

contrib/runit/meson.build

@@ -0,0 +1,17 @@
+runit = get_option('runit')
+
+runit_config_data = configuration_data()
+runit_config_data.set('LIBEXECDIR', join_paths(get_option('prefix'), get_option('libexecdir'), meson.project_name()))
+
+runit_config_data_file = configure_file(
+    input: 'run.in',
+    output: 'run',
+    configuration: runit_config_data
+)
+
+if runit
+    install_data(
+        runit_config_data_file,
+        install_dir: join_paths(get_option('sysconfdir'), 'runit', 'sv', 'tufmanager')
+    )
+endif

contrib/runit/run.in

@@ -0,0 +1,3 @@
+#!/bin/sh
+sv check dbus >/dev/null || exit 1
+exec @LIBEXECDIR@/tuf-server -f