templates/container-storage: Add a "this is generated" note

This is a best practice, and particularly in this case
when we're intending to modify a config file, it can't be identical
to the shipped version.

This avoids having libostree replace it with a newer version.

Closes: openshift#1319

templates/common/_base/files/container-storage.yaml

@@ -3,6 +3,8 @@ mode: 0644
 path: "/etc/containers/storage.conf"
 contents:
   inline: |
+    # This file is generated by the Machine Config Operator's containerruntimeconfig controller.
+    #
     # storage.conf is the configuration file for all tools
     # that share the containers/storage libraries
     # See man 5 containers-storage.conf for more information