Improve README.md

[sebgie]

Our current readme is very minimalistic (Changlog has more lines than Instructions) and doesn't really explain what is going on behind the curtain. For new contributors this is not very helpful since they are able to get a new VM up and running within minutes, but don't know how to customize it without reading Vagrant or Puppet documentation.

In my opinion it would be good to answer the the following list of questions along with install and usage instructions.

• What software is available on the VM?
• What services are running after vagrant up?
• How to start/stop/restart/provision an existing VM?
• What does vagrant ssh do?
• How to mount a custom directory? (see #72)
• Why would I want to use Ghost-Vagrant and how does it help my Ghost development?
• How to use the preconfigured SSL certificates?
• ...?

[stantond]

This would be very helpful