todo.md: add some kernel work to be done

TODO.md

@@ -53,6 +53,9 @@
 ## IMPROVEMENTS:
 - systemd/journalctl: use a less shit pager
   - there's an env var for it: SYSTEMD_PAGER? and a flag for journalctl
+- kernels: ship the same kernel on every machine
+  - then i can tune the kernels for hardening, without duplicating that work 4 times
+- zfs: replace this with something which doesn't require a custom kernel build
 
 ### security/resilience
 - validate duplicity backups!