docs/introduction: Note VMs vs baremetal

docs/manual/introduction.md

@@ -79,6 +79,13 @@ filesystem that supports hard links.  Note: OSTree will
 transparently take advantage of some BTRFS features if deployed
 on it.
 
+OSTree is orthogonal to virtualization mechanisms like AMIs and qcow2
+images, though it's most useful though if you plan to update stateful
+VMs in-place, rather than generating new images.
+
+In practice, users of "bare metal" configurations will find the OSTree
+model most useful.
+
 ## Atomic transitions between parallel-installable read-only filesystem trees
 
 Another deeply fundamental difference between both package