log if we exit bc another instance is up

src/main.c

@@ -176,8 +176,10 @@ int main(void) {
 	applog(LOG_DBG, "Compiled with %s", C_STD);
 
 	/* see if another instance is up, quit if it is */
-	if (get_instance_lock() < 0)
+	if (get_instance_lock() < 0) {
+		applog(LOG_ERR, "Another instance is already running. Exiting.");
 		return 0;
+	}
 
 	/* malloc memory for the struct */
 	struct sensors_t *sensors = malloc(sizeof(*sensors)); // no actual point in mallocing and it is ever so sligtly slower to access heap vs stack, but its cool