board/qemu/ppc-bamboo: use path to vmlinux image for copy and paste users

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
(cherry picked from commit ceb3dae264fa1bf4b4806dbc1507582c74eb36b1)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

board/qemu/ppc-bamboo/readme.txt

@@ -1,5 +1,5 @@
 Run the emulation with:
 
-qemu-system-ppc -nographic -M bamboo -kernel vmlinux -net nic,model=virtio-net-pci -net user # qemu_ppc_bamboo_defconfig
+qemu-system-ppc -nographic -M bamboo -kernel output/images/vmlinux -net nic,model=virtio-net-pci -net user # qemu_ppc_bamboo_defconfig
 
 The login prompt will appear in the terminal that started Qemu.