Add state statement in preamble

Author: kito-cheng

preamble.adoc

@@ -1,3 +1,36 @@
+
+ifeval::["{revlifecycle}" == "dev"]
+[WARNING]
+.This document is in the link:http://riscv.org/spec-state[Development state]
+====
+Assume everything can change.
+====
+endif::[]
+ifeval::["{revlifecycle}" == "stable"]
+[WARNING]
+.This document is in the link:http://riscv.org/spec-state[Stable state]
+====
+Assume anything could still change, but limited change should be expected.
+====
+endif::[]
+ifeval::["{revlifecycle}" == "frozen"]
+[WARNING]
+.This document is in the link:http://riscv.org/spec-state[Frozen state]
+====
+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.
+====
+endif::[]
+ifeval::["{revlifecycle}" == "ratified"]
+[WARNING]
+.This document is in the link:http://riscv.org/spec-state[Ratified state]
+====
+No changes are allowed. Any desired or needed changes can be the subject of
+a follow-on new extension. Ratified extensions are never revised.
+====
+endif::[]
+
 Contributors to all versions of the spec in alphabetical order:
 
 Alex Bradbury,