Add comment to make sure the incomplete slide is noticed.

doc/nextml2015/presentation.tex

@@ -1154,6 +1154,8 @@ The result is then sliced to obtain the pre-nonlinearity activations for i, f, $
     outputs of both LSTM to the logistic regression. (No solutions provided)
 \end{itemize}
 
+% I don't know how to fix this frame since it seems incomplete.
+
 Deep Learning Tutorial on LSTM: \url{http://deeplearning.net/tutorial/lstm.html}
 
 (It have the papers