update ssl documentation

Doc/library/ssl.rst

@@ -279,6 +279,15 @@ SSLSocket Objects
                 else:
                     raise
 
+.. method:: SSLSocket.unwrap()
+
+   Performs the SSL shutdown handshake, which removes the TLS layer
+   from the underlying socket, and returns the underlying socket
+   object.  This can be used to go from encrypted operation over a
+   connection to unencrypted.  The returned socket should always be
+   used for further communication with the other side of the
+   connection, rather than the original socket
+
 .. method:: SSLSocket.getpeercert(binary_form=False)
 
    If there is no certificate for the peer on the other end of the