sugestion for documentation

[luberti]

Maybe could be useful to add to the documentation a couple of issues that can be encountered with VirtualBox and Vagrant:

1. In windows you have to install VirtualBox using a paramtere from the ecommand line:

VirtualBox-5.0.10-104061-Win.exe -msiparams NETWORKTYPE=NDIS5

in order to avoid this issue: https://forums.virtualbox.org/viewtopic.php?f=6&t=70199))

2. On Intel processors you have to enable virtualization at the bios level in order to avoid crash at launch time with error "VT-x is not available" eeror message

[Tuurlijk]

Can you add this to the 'Known Problems' section in the readme? And then maybe send me a pull request?