add a readme

sample.c

@@ -1,24 +1,30 @@
 // This program simply loads a QOI file into Allegro
 // as a texture and then dumps the texture data as a PNG.
-// Take notice of lines 20 and 21. You only need to initialize
+// Take notice of lines 26 and 27. You only need to initialize
 // the QOI plugin (this registers the function hooks that Allegro
 // will use whenever you want to I/O on a filename ending in .qoi)
 // 
-// Compile the test program with:
-// gcc -o test allegro_qoi.c test.c -lallegro -lallegro_image -I./
+// Compile the sample program with:
+// gcc -o sample allegro_qoi.c sample.c -lallegro -lallegro_image -I./
+// Then run it with a QOI image as the first argument.
 // 
 // qoi.h should be inside of your include path.
 // Either place it here, or in your system's global includes.
 
+#include <stdio.h>
 #include <allegro5/allegro.h>
 #include <allegro5/allegro_image.h>
 #include "allegro_qoi.h"
 
-int main() {
+int main(int argc, char **argv) {
+	if (argc < 2) {
+		printf("Usage: sample <filename>\n");
+		return 0;
+	}
 	al_init();
 	al_init_image_addon();
 	al_init_qoi();
-	ALLEGRO_BITMAP* bmp = al_load_bitmap("sample.qoi");
+	ALLEGRO_BITMAP* bmp = al_load_bitmap(argv[1]);
 	al_save_bitmap("out.png", bmp);
 	return 0;
 }