README: tell people how to execute the built files

*** 122,132 ****
  
  Following this, you can build the kernel as far as we have it for ARM
  
  cd uts; dmake install
  
! You now have a lovely unix and boot_archive pair in bcm2835/unix (raspberry
! pi) and qvpb/unix (qemu versatilepb).  These should be booted with a kernel
! command line mimicing that of the boot_archive (regardless of the path of the
! unix you actually provide).  For example: kernel /platform/bcm2835/kernel/unix
! -Bconsole=text
  
--- 122,177 ----
  
  Following this, you can build the kernel as far as we have it for ARM
  
  cd uts; dmake install
  
! You now have a lovely unix and boot_archive pair in bcm2835/unix (Raspberry
! Pi) and qvpb/unix (qemu versatilepb).
  
+ Step 4) Boot
+ 
+ Now that you have the gate built, you can try to boot the kernel.  This is
+ where things diverge between qemu and the Raspberry Pi.
+ 
+ Booting qemu is very easy:
+ 
+ qemu-system-arm \
+         -kernel $PROTO/platform/qvpb/kernel/loader \
+         -initrd $PROTO/platform/qvpb/kernel/initrd \
+         -machine versatilepb \
+         -cpu arm1176 \
+         -m 512 \
+         -no-reboot \
+         -nographic \
+         -append 'kernel /platform/qvpb/kernel/unix -Bconsole=uart'
+ 
+ The loader and kernel messages should appear in the same terminal.
+ 
+ Booting on real hardware is a bit more involved.
+ 
+   a) Create a FAT16 or FAT32 partition on the SD card.  You'll want it to be
+      at least 40 MB.
+ 
+   b) Create a config.txt on the partition:
+ 
+         gpu_mem=64
+         kernel=loader
+         initramfs initrd 0x00800000
+ 
+   c) Create a cmdline.txt on the partition:
+ 
+         kernel /platform/bcm2835/kernel/unix -Bconsole=uart
+ 
+   d) Place Raspberry Pi firmware onto the partition.  You can download
+      latest firmware from
+      https://github.com/raspberrypi/firmware/tree/master/boot. The firmware
+      from January 24th, 2015 is known to work.
+ 
+         0e52c8cdbfd21631746d6fcdc8f2750af39f4287  bootcode.bin
+         aba25d795eaddafd5c8ece3de18873b9928eb6f7  fixup_cd.dat
+         38e55d60f896738eec30d0ca4f62b68e48e99184  fixup.dat
+         4867e6eab84bb4138e812993112b6a05b7930b89  fixup_x.dat
+         fa993851acba366d9e37d59a1d9e9de84b19173f  start_cd.elf
+         356060e0f44742d8835294a211b812efcac29f66  start.elf
+         b7f01f90d995a36c9d765fd1f4d95a5fcdfd7e41  start_x.elf
+ 
+   e) Copy $PROTO/platform/bcm2835/kernel/{loader,initrd} onto the partition.