Update usage section with an example
The example has been copied from okeanos-guides. However, some
of the example's steps have been ommited (e.g. the installation of
snf-image-creator). Also, the focus has been shifted from ~okeanos to a
run-of-the-mill synnefo deployment.
- [DH] docs/snapshots/custom-vm.png
- [DH] docs/snapshots/image-creator.png
- [DH] docs/snapshots/mkimage-fin.png
- [DH] docs/snapshots/mkimage-results.png
- [DH] docs/snapshots/mkimage-wizard.png
- [DH] docs/snapshots/mkimage1.png
- [DH] docs/snapshots/mkimage2.png
- [DH] docs/snapshots/mkimage3.png
- [DH] docs/snapshots/mkimage4.png
- [DH] docs/snapshots/qemu-live.png
- [DH] docs/snapshots/qemu-partition.png