Add docs on enabling collaborator_groups feature
Add docs on enabling collaborator_groups feature

This is a highly demanded feature implemented in a recent version of Supermarket. There's a lot of information on how to use it, but nothing about enabling it.
irvingpop/supermarket-omnibus-cookbook,chef-cookbooks/supermarket-omnibus-cookbook,nellshamrell/supermarket-omnibus-cookbook,GannettDigital/chef-supermarket-omnibus-cookbook