Add docs for os.fchdir().
diff --git a/Doc/lib/libos.tex b/Doc/lib/libos.tex
index 6a07ab1..5819f80 100644
--- a/Doc/lib/libos.tex
+++ b/Doc/lib/libos.tex
@@ -101,6 +101,7 @@
\end{datadesc}
\begin{funcdescni}{chdir}{path}
+\funclineni{fchdir}{}
\funclineni{getcwd}{}
These functions are described in ``Files and Directories'' (section
\ref{os-file-dir}).
@@ -590,6 +591,14 @@
Availability: Macintosh, \UNIX, Windows.
\end{funcdesc}
+\begin{funcdesc}{fchdir}{fd}
+Change the current working directory to the directory represented by
+the file descriptor \var{fd}. The descriptor must refer to an opened
+directory, not an open file.
+Availability: \UNIX.
+\versionadded{2.3}
+\end{funcdesc}
+
\begin{funcdesc}{getcwd}{}
Return a string representing the current working directory.
Availability: Macintosh, \UNIX, Windows.