chdir.2: Add ENOTDIR error for fchdir()

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
diff --git a/man2/chdir.2 b/man2/chdir.2
index 87fc141..88f4184 100644
--- a/man2/chdir.2
+++ b/man2/chdir.2
@@ -124,6 +124,10 @@
 .B EBADF
 .I fd
 is not a valid file descriptor.
+.TP
+.B ENOTDIR
+.I fd
+does not refer to a directory.
 .SH CONFORMING TO
 POSIX.1-2001, POSIX.1-2008, SVr4, 4.4BSD.
 .SH NOTES