Update docs to show how to pull from multiple organizations via robot tokens on OpenShift

Quay robot tokens do not span organizations.  Some users however do want to pull across organizations using robot tokens.  OpenShift permits multiple namespaces to be provided within a `dockerconfigjson` secret so this can theoretically be done via a single service account.  For example:

{
   "auths": {
     "quay.io/org1":
{       "auth": "super secret",       "email": ""     }
,
     "quay.io/org2":
{       "auth": "even more secret",       "email": ""     }
,
     "quay.io/org3":
{       "auth": "oh-la-la-dont-look",       "email": ""     }
  }
 }

The single SA can then be used across Kube namespaces as needed to overcome the token scoping limitation.  Docs should reflect this technique as a workaround for robot token scoping within a single namespace.

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