docs: Add constant bit flag to operands

Signed-off-by: Ronald Caesar <github43132@proton.me>

src/IR_DESIGN_DOC.md

@@ -169,6 +169,10 @@ ssa_version_t ssa_versions[???];
 
 <**opc**>   10-bit opcode.
 
+### Operational Information
+
+If Bit[17] in `src1`, `src2`, or `src` is 1, the operand is a raw number.  It has not SSA index. It has no entry in `ssa_versions`.
+
 ## Instruction Design
 
 ```c