(WIP) Mention possibility of entirely different root layouts

This is for situations where different packages are results of
different projects / supply chains.

Signed-off-by: Aditya Sirish <[email protected]>

ITE/2/README.adoc

@@ -176,9 +176,13 @@ from that for another package. This MAY be done in a number of different
 ways, but perhaps the simplest is to use directories with unique names to
 isolate different in-toto link metadata for different packages, where the
 name MAY be the SHA-256 hash of the "`developer`" step link metadata file
-for a particular package. The root layout MAY be identical for each
-of these packages, but it can differ to allow for changes in the supply
-chain such as changes in functionaries' keys.
+for a particular package. The root layouts MAY be identical for each
+of these packages where they are all the results of the same supply chain.
+The root layouts MAY differ to allow for changes in the supply chain (such
+as revoking functionaries' keys), or even to account for packages that are
+from entirely different supply chains (therefore, with entirely different
+root layouts). By using consistent snapshots and defining custom targets
+metadata, backward compatibility can be maintained.
 . The targets metadata MUST also list the targets metadata of all
 in-toto link metadata files associated with all available packages. Note
 that as the number of packages grows, so will the size of this metadata