Document missing opcodes.

Doc/lib/libdis.tex

@@ -126,6 +126,10 @@ instructions.
 Indicates end-of-code to the compiler, not used by the interpreter.
 \end{opcodedesc}
 
+\begin{opcodedesc}{NOP}{}
+Do nothing code.  Used as a placeholder by the bytecode optimizer.
+\end{opcodedesc}
+
 \begin{opcodedesc}{POP_TOP}{}
 Removes the top-of-stack (TOS) item.
 \end{opcodedesc}
@@ -396,6 +400,10 @@ is the address to jump to (which should be a \code{FOR_ITER}
 instruction).
 \end{opcodedesc}
 
+\begin{opcodedesc}{LIST_APPEND}{}
+Calls \code{list.append(TOS1, TOS)}.  Used to implement list comprehensions.
+\end{opcodedesc}
+
 \begin{opcodedesc}{LOAD_LOCALS}{}
 Pushes a reference to the locals of the current scope on the stack.
 This is used in the code for a class definition: After the class body