Clarify doc: API is admin only
Clarify doc: API is admin only

Clarify wording in the architecture doc page that Ironic's API service
is intended only for privileged (admin) users and privileged
services in the control plane.

Change-Id: I2e660401c7e2ebe2f6dc89673236107727462fcc

rackerlabs/ironic,naototty/vagrant-lxc-ironic,naototty/vagrant-lxc-ironic,ramineni/myironic,bacaldwell/ironic,NaohiroTamura/ironic,bacaldwell/ironic,supermari0/ironic,SauloAislan/ironic,froyobin/ironic,devananda/ironic,pshchelo/ironic,redhat-openstack/ironic,pshchelo/ironic,openstack/ironic,dims/ironic,ionutbalutoiu/ironic,hpproliant/ironic,Tan0/ironic,rdo-management/ironic,ionutbalutoiu/ironic,dims/ironic,NaohiroTamura/ironic,faizan-barmawer/openstack_ironic,debayanray/ironic_backup,SauloAislan/ironic,naterh/ironic,Tehsmash/ironic,openstack/ironic