Update Vagrant setup instructions

longb4@cf416-19 ~/code/WWUDevOpsVagrant
$ vagrant up
Bringing machine 'default' up with 'virtualbox' provider...
[default] Running triggers before up...
[default] Setting Virtualbox default machine directory to /tmp...
[default] Executing command "VBoxManage setproperty machinefolder /tmp"...
[default] Error: VAGRANT_HOME is /tmp/longb4-vagrant.d/!
[default] Add export 'VAGRANT_HOME=/tmp/$USER-vagrant.d' to your .bashrc