Add NOTE that only G-stage PBMTs apply to VS-stage PTE accesses (riscv#1688)

Author: aswaterman

src/supervisor.adoc

@@ -2130,6 +2130,11 @@ bits override the intermediate attributes to produce the final set of
 attributes used by accesses to the page in question. Otherwise, the
 intermediate attributes are used as the final set of attributes.
 
+NOTE: These final attributes apply to implicit and explicit accesses that
+are subject to both stages of address translation.
+For accesses that are not subject to the first stage of address translation,
+e.g. VS-stage page-table accesses, the intermediate attributes apply instead.
+
 [[svinval]]
 == "Svinval" Extension for Fine-Grained Address-Translation Cache Invalidation, Version 1.0