nubus: add comment indicating reference documents

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <20210924073808.1041-2-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

hw/nubus/nubus-bus.c

@@ -8,6 +8,14 @@
  *
  */
 
+/*
+ * References:
+ *   Nubus Specification (TI)
+ *     http://www.bitsavers.org/pdf/ti/nubus/2242825-0001_NuBus_Spec1983.pdf
+ *
+ *   Designing Cards and Drivers for the Macintosh Family (Apple)
+ */
+
 #include "qemu/osdep.h"
 #include "hw/nubus/nubus.h"
 #include "qapi/error.h"