Add instructions to install "bowl" command.
Add section on routing from local machine to VM

Nick and I found it unclear how requests originating from outside the VM
are routed to the individual apps. This explains how and why to add a
hostname entry.
Add a description of what bowl does

It wasn't clear what bowl did or that it used the Pinfile, or that you
can start ie backdrop_read and backdrop_write individually.
Advise getting VM IP from Vagrantfile

The Vagrantfile defines the IP. The user should look there first.
Correct a nonsense URL

admin.perfplat.dev/data is invalid; that URL isn't valid for admin.*
Merge pull request #8 from alphagov/update-readme

Update README