Nothing in bin should rely on bundler

This is probably why the gem isn't working - the 'bundler/setup' will configure a gemset based on the Gemfile found in whatever directory you happen to be in when you call it.  If that Gemfile doesn't include vcloud-walker, then the later require won't find anything.
Update README now it's a gem
Merge pull request #57 from alphagov/fix-gem

[#62889568] Nothing in bin should rely on bundler