add preferences key to ui chapter

doc/chapter/3ui.tex

@@ -81,7 +81,8 @@ These can also be used by clicking on one of the buttons displayed in figures~\r
         Ensures that the generated graph is connected.\\\hline
         Alt + S & Save the current graph to a file (opens a dialog window). \\\hline
         Alt + L & Load a graph from a file (opens a dialog window). \\\hline
-        Alt + D & Show a debug table (opens window~\ref{fig:debug-table}). \\\hline
+        Alt + D & Show a debug table (opens window~\ref{fig:debug-table}) and also printlines its content. \\\hline
+        Alt + O & Opens the preferences dialog~\ref{fig:preferences}. \\\hline
         \caption[Overview of the available keyboard commands]{Overview of the available keyboard commands.
         The lazy user might not want to learn these by rote but instead use the buttons displayed in figures~\ref{fig:sketch} and~\ref{fig:full-application-example}.}
         \label{table:keys}

doc/chapter/appendix.tex

@@ -40,6 +40,13 @@
     \label{fig:debug-table}
 \end{figure}
 
+\begin{figure}[htp]
+    \centering
+    \includegraphics[width=0.33\linewidth]{img/preferences}
+    \caption[Preferences]{The dialog for adjusting the preferences.}
+    \label{fig:preferences}
+\end{figure}
+
 \begin{figure}[htp]
     \centering
     \includegraphics[width=0.33\linewidth]{img/error_disconnected}