bug #1444104: add note about fdopen() to os.open().
diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index 8c4b770..a9100a1 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -547,7 +547,8 @@
This function is intended for low-level I/O. For normal usage,
use the built-in function \function{open()}, which returns a ``file
object'' with \method{read()} and \method{write()} methods (and many
-more).
+more). To wrap a file descriptor in a ``file object'', use
+\function{fdopen()}.
\end{notice}
\end{funcdesc}