update to mention sdl deps

README.md

@@ -60,6 +60,7 @@ Compilation and use
 This is very old software, but as all good C code, it works ten and twenty years thereafter. I have successfully compiled it,
 booted a BK-0010.01 machine and played a game under Ubuntu 13.05, Linux 3.8.5 and libSDL 1.2.
 
+* Make sure libsdl1.2 and its -dev packages are installed
 * Edit the Makefile to correct the path to your libSDL.so 
 * Run `make`
 * Run `./bk -?` for overview of emulation modes