Flesh out description of getlogin() and recommend against using it.
diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index 4220d6d..7a63890 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -139,8 +139,9 @@
\end{funcdesc}
\begin{funcdesc}{getlogin}{}
-Return the actual login name for the current process, even if there
-are multiple login names which map to the same user id.
+Return the name of the user logged in on the controlling terminal of
+the process. For most purposes, it is more useful to use the
+environment variable \envvar{LOGNAME} to find out who the user is.
Availability: \UNIX.
\end{funcdesc}