Note whether clusters are by request on cluster views

[ajeanmahoney]

Sometimes clusters are requested rather than being based on normative reference dependencies. Pages that talk about clusters should note if the cluster was by request.

Cluster NNN

draft-ietf-dog-blah
   Normative reference to draft-ietf-dog-foo

draft-ietf-dog-foo
   No normative reference dependencies. Added to Cluster NNN at the request of Jo Smith (pets AD).