add missing description of os.extsep
diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index 70da201..d963056 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -1643,6 +1643,11 @@
backslash.
\end{datadesc}
+\begin{datadesc}{extsep}
+The character which separates the base filename from the extension,
+e.g. \character{.} in \code{os.py}.
+\end{datadesc}
+
\begin{datadesc}{pathsep}
The character conventionally used by the operating system to separate
search patch components (as in \envvar{PATH}), such as \character{:} for