mention MANPATH

Author: vladak

intro.tex

@@ -398,7 +398,8 @@
 \item The \texttt{man} command uses a list of system directories to search for
 man pages.  If you have manual pages someplace else, perhaps in a local subtree
 after you unpacked a tar file you downloaded and you want to check the
-documentation, the \texttt{-M} option may come in handy.
+documentation, the \texttt{-M} option or the \texttt{MANPATH} environment
+variable may come in handy.
 \item Sometimes there are entries for the same name in several sections.  If
 unsure what you are looking for, use the \texttt{-a} option to get all manual
 pages for that name (otherwise you get just one, usually from the first