Update tuf-spec.md

Co-Authored-By: Trishank Karthik Kuppusamy <[email protected]>

tuf-spec.md

@@ -1303,7 +1303,7 @@ non-volatile storage as FILENAME.EXT.
    2.root.json that has threshold 3, 2.root.json MUST be signed by at least 2
    keys defined in 1.root.json and at least 3 keys defined in 2.root.json. The
    client starts the root key update process with the latest version of root
-   metadata available on the client, and stops when no newer root metadata is
+   metadata available on the client, and stops when no version N+1 (where N is the latest trusted version) of the root metadata is
    available from the repository. This ensures that an outdated client can
    always correctly re-trace the chain of trust across multiple root key
    updates, even if the latest set of root keys on the client dates back