Do not require rb-notify (temporary until we can upgrade middleman)
Update to the latest bundle to fix rubyracer issues
Add a note that VirtualBox supports parallelization
Add a note that VMWare does not support parallelization at this time
Add a note to check the docs
VirtualBox does not support it either
Merge pull request #4653 from mitchellh/sethvargo/document_parallel

website: vmware does not support --parallel