Set flag to create folder /vagrant/code if it doesn't exist

On first run of vagrant up the following error was occurring
* Shared folder host path for 'code' doesn't exist: code
Update instructions for building and installing module

Use 'build' as parameter for ./go instead of 'package'
Changed directory in which *.omod file is found
Merge pull request #8 from cathy-mcdonald/master

Fixes to minor issues