README: Add warning about ssh -Y

README

@@ -13,7 +13,8 @@ OSDD is a simple daemon whose purpose is to wait for messages sent by other
 programs and display them on the screen using libxosd. Unlike other such
 daemons, it handles message attributes (like colors), keeps its eye on
 message timing and uses X properties to pass messages, so it works over SSH
-connections with X forwarding.
+connections with X forwarding (however, you need to use "ssh -Y" instead of
+"ssh -X" with newer versions of OpenSSH).
 
 I have developed osdd on Linux, but it should work on any recent POSIX-compliant
 system equipped with libX11 and libxosd.