Need to document required BIG-IP user roles
Need to document required BIG-IP user roles

Problem:
It is not clear what types of BIG-IP user roles are allowed
for the Marathon controller.

Solution:
Document the required roles the controller requires for the
BIG-IP user.

affects-branches: master, 1.1-stable

michaeldayreads/marathon-bigip-ctlr,michaeldayreads/marathon-bigip-ctlr,michaeldayreads/marathon-bigip-ctlr