Sync dirs

If a user doesn't read the readme (like me doh!) then the `vagrant up` fails because the sync directories don't exist. I've made a few changes to avoid this issue.

- Changed host directory locations to be local and referenced them with relative paths. This allows the project to be self-contained.
- Added some simple ruby to the top of the `Vagrantfile` to check for the existence of the sync directories and create them if required. This avoids the need for any manual config before use.
- Changed the `readme.md` to reflect the above.