Add Hypervisor-level to the table in the Subset Naming section.

Author: topperc

src/naming.adoc

@@ -203,6 +203,10 @@ e.g., RV32IMACV is legal, whereas RV32IMAVC is not.
 
 |Supervisor-level extension "def" |Ssdef |
 
+3+|*Standard Hypervisor-Level Extensions*
+
+|Hypervisor-level extension "ghi" |Shghi |
+
 3+|*Standard Machine-Level Extensions*
 
 |Machine-level extension "jkl" |Smjkl |