add a note about the undocumented bsddb185 module
diff --git a/Doc/lib/libundoc.tex b/Doc/lib/libundoc.tex
index c1e3760..09402b5 100644
--- a/Doc/lib/libundoc.tex
+++ b/Doc/lib/libundoc.tex
@@ -62,6 +62,12 @@
--- Implementation on \module{os.path} on \POSIX.
\end{description}
+\item[\module{bsddb185}]
+--- Backwards compatibility module for systems which still use the Berkeley
+DB 1.85 module. It is normally only available on certain BSD Unix-based
+systems. It should never be used directly.
+\end{description}
+
\section{Multimedia}