feat(wpcarro/blog): Create short post about scheduled reboots

Slowly building the habit of blogging more (especially about nix).

Change-Id: I13006a6555d746ab55b4b282ea83bc732573a58e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5149
Tested-by: BuildkiteCI
Reviewed-by: wpcarro <wpcarro@gmail.com>
Autosubmit: wpcarro <wpcarro@gmail.com>

users/wpcarro/website/blog/posts/auto-reboot-nixos.md

@@ -0,0 +1,40 @@
+## Show me the codes
+
+Regularly rebooting machines can be a useful, hygienic practice, but quite
+frankly I cannot be relied on to remember to regularly reboot my machine.
+
+Let's free-up some wetware-RAM by automating this with Nix. The following
+addition to your `configuration.nix` will schedule daily reboots at `03:00`:
+
+```nix
+systemd.timers.auto-reboot = {
+  wantedBy = [ "timers.target" ];
+  timerConfig = {
+    OnCalendar = "*-*-* 03:00:00";
+    Unit = "reboot.target";
+  };
+};
+```
+
+If you want to fiddle with the date format, `systemd-analyze` is your friend:
+
+```shell
+λ systemd-analyze calendar '*-*-* 03:00:00'
+Normalized form: *-*-* 03:00:00
+    Next elapse: Tue 2022-02-01 03:00:00 PST
+       (in UTC): Tue 2022-02-01 11:00:00 UTC
+       From now: 12h left
+```
+
+After calling `nixos-rebuild switch`, you can verify that `systemd` started the
+timer with:
+
+```shell
+λ systemctl list-timers auto-reboot
+#  output omitted because I'm writing this from a different machine
+```
+
+## That's all, folks!
+
+I wanted to keep this post short-and-sweet, to build the habit of posting more
+regularly. Hopefully someone out there found this useful.