Mention that you need the X11 devel files.
diff --git a/README b/README
index 306fc9f..c6542fc 100644
--- a/README
+++ b/README
@@ -48,6 +48,9 @@
the ports tree:
ftp://ftp.freebsd.org/pub/FreeBSD/FreeBSD-current/ports/emulators/wine/files/
+You need to have the X11 development include files installed
+(called xlib6g-dev in Debian and XFree86-devel-4.0.1-1 in RedHat).
+
You also need to have libXpm installed on your system. The sources for
it are available at ftp.x.org and all its mirror sites in the directory
/contrib/libraries. If you are using RedHat, libXpm is distributed as the
