Fix header and add lacking instructions to readme.
--- a/main.c
+++ b/main.c
@@ -8,3 +8,3 @@
 #ifdef ENABLE_SOUND
-#include <SDL_Mixer.h>
+#include <SDL_mixer.h>
 static int soundv = 2;
--- a/readme
+++ b/readme
@@ -6,2 +6,4 @@
 
+use -nosound to disable sound
+
 I knocked this game up over a couple of days, and can't be