update bk example

doc/chapter/3ui.tex

@@ -52,7 +52,8 @@ Figure~\ref{fig:originalpapergraph} compares our results to those of Brandes and
         \includegraphics[width=0.4\linewidth]{img/bk-example-ours}
         \caption[The same graph as~\ref{fig:theirs}, displayed by \appname.]{The same graph as~\ref{fig:theirs}, displayed by \appname.
         The layouts are leftmost (first column), rightmost (third column), upper (first row) and lower (third row), respectively.
-        The balanced layout is in the center.}
+        The balanced layout is in the center.
+        The narrower nodes are dummy nodes.}
         \label{fig:ours}
     \end{subfigure}\\\vspace{4mm}
     \caption[Comparison to Brandes and Köpf]{Comparison of the implementation to the results of Brandes and Köpf~\cite{brandes_fast_2001}}