fix typo

Author: Vladimir Kotal

intro.tex

@@ -154,7 +154,7 @@
     \end{itemize2}
 \item \emsl{POSIX} (Portable Operating System based on UNIX)
     \begin{itemize2}
-    \item family or standards published by the IEEE organization marked
+    \item family of standards published by the IEEE organization marked
     P1003.xx, gradually incorporated into ISO standards
     \end{itemize2}
 \item \emsl{XPG} (X/Open Portability Guide)