Added comment about CBC mode

Author: MHumm

Source/DECZIPHelper.pas

@@ -84,7 +84,7 @@ function CreateZIPCryptoAlgorithmInstance(AlgorithmID: UInt16):TDECFormattedCiph
   end;
 
   if Assigned(Result) then
-    Result.Mode := cmCBCx;
+    Result.Mode := cmCBCx; // as per ZIP documentation the only supported mode
 end;
 
 end.