README: Clarify misleading knife.rb snippet
README: Clarify misleading knife.rb snippet

The previous README.md was suggesting setting an auth URL that would not work when `$OS_AUTH_URL` comes from an openrc file.  This change should remove this little trap. :)
chef/knife-openstack,BobbyRyterski/knife-openstack,chef/knife-openstack,david-crowder/knife-openstack