tier-0: Tweak some comments

tier-0/manifest.yaml

@@ -1,4 +1,7 @@
 edition: "2024"
+# Basically we need to have a stub /etc/machine-id
+# so that Anaconda and especially `systemctl enable`
+# in our container builds do the right thing.
 # https://github.com/CentOS/centos-bootc/issues/167
 machineid-compat: true
 # Be minimal
@@ -14,7 +17,7 @@ etc-group-members:
   - systemd-journal
   - adm
 
-# Default to `bash` in our container, the same as other containers we ship.
+# This is an opinionated default to run systemd.
 container-cmd:
   - /sbin/init