fix a underscore in normal text, it has to be escaped

doc/handbook/5_scripts.tex

@@ -37,6 +37,6 @@ In order to ensure consistency when developing in dumux, developers are encourag
 \subsection{Miscellaneous:} \label{ssec:miscScripts}
 In addition, a few miscellaneous scripts are available.
 \begin{itemize}
-	\item Parameter scripts: The script \texttt{doc/generate_parameterlist.py} is available for tracking all of the runtime parameters used.
+	\item Parameter scripts: The script \texttt{doc/generate\_parameterlist.py} is available for tracking all of the runtime parameters used.
 	\item Other: \texttt{doc/getcontributors.sh} can be used to find the names and contact information for all commit authors over a given time period. 
 \end{itemize}