fix spelling

Author: Vladimir Kotal

intro.tex

@@ -2084,7 +2084,7 @@
 should be lower case, 2--9 characters long and using only characters from
 the portable character set. Arguments without options should be possible to group
 after '--', etc.
-\item Using numbers for options (ala \texttt{-4} and \texttt{-6} for some
+\item Using numbers for options (e.g. \texttt{-4} and \texttt{-6} in some
 \texttt{ping} implementations) is old fashioned;
 reportedly SUSv3 mentions that.
 \item Watch out for GNU command line utilities and their strange permutations