Update header.adoc

Signed-off-by: Rafael Sene <[email protected]>

Author: rpsene

header.adoc

@@ -39,11 +39,9 @@ endif::[]
 
 // Preamble
 [WARNING]
-.This document is in the link:http://riscv.org/spec-state[Frozen state]
+.This document is link:http://riscv.org/spec-state[Ratified]
 ====
-Change is extremely unlikely.
-A high threshold will be used, and a change will only occur because of some truly critical issue being identified during the public review cycle.
-Any other desired or needed changes can be the subject of a follow-on new extension.
+No changes are allowed. Any desired or needed changes can be the subject of a follow-on new extension. Ratified extensions are never revised
 ====
 
 [preface]