fix Makefile and README.md for 2006/monge

NOTE: While this code compiled, it did not link.

This code may have been written for sdl-config instread of
sdl2-config.

2006/monge/Makefile

@@ -105,7 +105,7 @@ CDEFINE=
 #CINCLUDE= -include stdlib.h
 #CINCLUDE= -include stdio.h
 #CINCLUDE= -include stdlib.h -include stdio.h
-#CINCLUDE= -I ${X11_INCDIR}
+#CINCLUDE= -I ${X11_INCDIR} -I ${X11_INCDIR}/X11
 CINCLUDE= `${SDL2_CONFIG} --cflags`
 
 # Optimization