Add notes about running Raspberry Pi VM with qemu.

README_raspberrypi.txt

@@ -6,11 +6,31 @@ cd build
 cmake .. -DCMAKE_TOOLCHAIN_FILE=../cmake/Toolchain-raspberrypi.cmake
 make
 
-Notes
------
+Virtual machine
+---------------
 
 Building with a cross compiler is not yet documented. Building directly
 on a Raspberry Pi or in a Raspberry Pi VM is very similar to building on
 "regular" Linux. apt-get install the -dev packages you need, run cmake and
 make sure everything you need is found.
 
+For example, you can use an image from:
+
+    http://www.raspberrypi.org/downloads
+
+and a kernel:
+
+    http://xecdesign.com/downloads/linux-qemu/kernel-qemu
+
+With a qemu command line like:
+
+    qemu-system-arm -kernel kernel-qemu -cpu arm1176 -m 256 -M versatilepb \
+        -no-reboot -serial stdio -append "root=/dev/sda2 panic=1" \
+        -hda 2012-12-16-wheezy-raspbian.img \
+        -redir tcp:2222::22 -net nic -net user
+
+You can ssh into the VM with:
+
+    ssh -p 2222 [email protected]
+
+Within the guest you can access the host at 10.0.2.2.