add section for class diagrams

doc/chapter/2architecture.tex

@@ -86,4 +86,7 @@ The structure is as follows:
     \end{lstlisting}
     \caption[Example Input File]{Example Input file that is understood by \appname.}
     \label{fig:json-example}
-\end{figure}
+\end{figure}
+
+\section{Class Diagrams}\label{sec:classDiagrams}
+\TODO{run vpp}