chore(package): make sure 'nobody' user & group exists on the target system

contrib/afterinstall.sh

@@ -1 +1,6 @@
+export USER="nobody"
+export GROUP="nobody"
+id -u $USER &>/dev/null || useradd $USER
+id -u $GROUP &>/dev/null || useradd $GROUP
+
 systemctl daemon-reload