fix wording

Author: Vladimir Kotal

intro.tex

@@ -2070,7 +2070,7 @@
 \item common notation for shell: \verb#program -option arguments#
 \item options are in the form of \texttt{-x} or \texttt{-x \emph{value}},
 where \texttt{x} is alphanumeric, \texttt{\emph{value}} is an arbitrary string
-\item multiple options can be unified: \texttt{ls -lRa}
+\item multiple options can be grouped: \texttt{ls -lRa}
 \item '\texttt{--}' or first argument not starting with '\texttt{-}'
 marks the end of options and arguments following are not considered options even
 if they start with '\texttt{-}'.