add pre-ratification warnings to Zimop and Zcmop

src/zimop.adoc

@@ -1,5 +1,12 @@
 [[zimop]]
 == "Zimop" May-Be-Operations Extension, Version 0.1
+
+[WARNING]
+====
+*Warning! This stable specification may change before being accepted as
+a standard by RISC-V International.*
+====
+
 This chapter defines the "Zimop" extension, which introduces the concept of
 instructions that _may be operations_ (MOPs).  MOPs are initially defined to
 simply write zero to `x[rd]`, but are designed to be redefined by later
@@ -62,10 +69,14 @@ MOP may impose such a requirement.
 NOTE: Not carrying a syntactic dependency relieves straightforward
 implementations of reading `x[rs1]` and `x[rs2]`.
 
-<<<
-
 === "Zcmop" Compressed May-Be-Operations Extension, Version 0.2
 
+[WARNING]
+====
+*Warning! This stable specification may change before being accepted as
+a standard by RISC-V International.*
+====
+
 This section defines the "Zcmop" extension, which defines eight 16-bit MOP
 instructions named C.MOP.__n__, where __n__ is an odd integer between 1 and
 15, inclusive.  C.MOP.__n__ is encoded in the reserved encoding space