Add a note.

Change-Id: I55362cbc8bfbb22ebcd493db7cdeb34fc3394e3a
diff --git a/vm/mterp/x86-atom/TODO.txt b/vm/mterp/x86-atom/TODO.txt
index b557be4..99d25a7 100644
--- a/vm/mterp/x86-atom/TODO.txt
+++ b/vm/mterp/x86-atom/TODO.txt
@@ -8,6 +8,8 @@
      skip a memory load when debugger support is completely disabled)
 (hi) WITH_DEBUGGER and WITH_PROFILER are no longer defined (but are
      assumed to be enabled)
+(hi) Implement OP_DISPATCH_FF for real. (Right now it's treated as
+     an unused instruction.)
 
 (md) Correct OP_MONITOR_EXIT (need to adjust PC before throw)
 (md) OP_THROW needs to export the PC