Bug #1460564: document that socket.fromfd() duplicates the given
file descriptor.
diff --git a/Doc/lib/libsocket.tex b/Doc/lib/libsocket.tex
index 04d467a..c7b656d 100644
--- a/Doc/lib/libsocket.tex
+++ b/Doc/lib/libsocket.tex
@@ -317,10 +317,11 @@
\end{funcdesc}
\begin{funcdesc}{fromfd}{fd, family, type\optional{, proto}}
-Build a socket object from an existing file descriptor (an integer as
-returned by a file object's \method{fileno()} method). Address family,
-socket type and protocol number are as for the \function{socket()} function
-above. The file descriptor should refer to a socket, but this is not
+Duplicate the file descriptor \var{fd} (an integer as returned by a file
+object's \method{fileno()} method) and build a socket object from the
+result. Address family, socket type and protocol number are as for the
+\function{socket()} function above.
+The file descriptor should refer to a socket, but this is not
checked --- subsequent operations on the object may fail if the file
descriptor is invalid. This function is rarely needed, but can be
used to get or set socket options on a socket passed to a program as