Mention devmem2 on platform device

kernel_module/platform_device.c

@@ -9,6 +9,12 @@ Expected outcome after insmod:
 
 - QEMU reports MMIO with printfs
 - IRQs are generated and handled by this module, which logs to dmesg
+
+Also without insmodding this module, try:
+
+	devmem2 0x101e9000 w 0x12345678
+
+which touches from userland through /dev/mem.
 */
 
 #include <linux/init.h>