Write a short HowTo for Omistack users

the document should include:

• login in (duh!)
• creating a network
• configuring a subnet with DHCP and DNS server entries
• starting a VM from one of the presets with an image
• assigning a network and a floating IP to a VM
• using the web console to administrate the VM
• maybe also mention howto use ssh with pubkey on a machine with a floating ip
• correctly deleting VMs and networks (deleting ports, and subnets first)
• common bugs and error messages we already encountered should be mentioned