Minor doc tweaks

docs/book/tools.tex

@@ -215,6 +215,8 @@ \section{parallel\_stereo}
 (stop at the stage {\it right before} this value). \\ \hline
 \texttt{-\/-corr-seed-mode integer(=0 to 3)} & Correlation seed strategy
 (section \ref{corr_section}). \\ \hline
+\texttt{-\/-sparse-disp-options \textit{string} } & Options to pass directly
+to sparse\_disp (section \ref{sparse-disp}). \\ \hline
 \end{longtable}
 
 \subsection{Advanced usage}