Update bootc-fetch-apply-updates.timer with comments for RandomizedDe…

…laySec=

RandomizedDelaySec= is the best kept secret of timers. Given that such few people know about it and it's very useful for large deployments, I think it makes sense to add it as a comment.

systemd/bootc-fetch-apply-updates.timer

@@ -7,6 +7,8 @@ ConditionPathExists=/run/ostree-booted
 OnBootSec=1h
 # This time is relatively arbitrary and obviously expected to be overridden/changed
 OnUnitInactiveSec=8h
+# When deploying a large number of systems it's recommended to randomize this timer to a degree to help with load.
+#RandomizedDelaySec=2h
 
 [Install]
 WantedBy=timers.target