add category descriptions

diff --git a/simple_v_extension/opcodes.mdwn b/simple_v_extension/opcodes.mdwn
index 1bcf29253c72eae9ea51c754778bebda81186819..efe05fbcf1a8a45f480efb6022bed298b00463e4 100644 (file)
--- a/simple_v_extension/opcodes.mdwn
+++ b/simple_v_extension/opcodes.mdwn
@@ -6,6 +6,9 @@ page categorises and identifies the type of parallelism that SimpleV
 indirectly adds on each RISC-V **standard** opcode.  These are note-form:
 see [[specification]] for full details.
 
+Note that the list is necessarily incomplete, as any custom or future
+extensions may also benefit from fitting one of the categories below.
+
 * **-** no change of behaviour takes place: operation remains
   **completely scalar** as an **unmodified**, unaugmented standard RISC-V
   opcode, even if it has registers.