Add configuring docs for oc-id.
Add configuring docs for oc-id.

The CHEF_OAUTH2_SITE docs are a little vague because it is not intended to be
used. It could be removed, as I do not think that other organizations using
Supermarket would standup their own OAuth2 provider that replicates oc-id, but
you never know.

nellshamrell/supermarket,dpnl87/supermarket,dpnl87/supermarket,tas50/supermarket,rafaelmagu/supermarket,tas50/supermarket,leftathome/supermarket,chef/supermarket,chef/supermarket,rafaelmagu/supermarket,leftathome/supermarket,robbkidd/supermarket,dpnl87/supermarket,chef/supermarket,nellshamrell/supermarket,jzohrab/supermarket,jzohrab/supermarket,chef/supermarket,nellshamrell/supermarket,rafaelmagu/supermarket,chef/supermarket,juliandunn/supermarket,tas50/supermarket,jzohrab/supermarket,leftathome/supermarket,tas50/supermarket,rafaelmagu/supermarket,juliandunn/supermarket,juliandunn/supermarket,robbkidd/supermarket,robbkidd/supermarket,leftathome/supermarket,jzohrab/supermarket,dpnl87/supermarket,robbkidd/supermarket,nellshamrell/supermarket,juliandunn/supermarket