Update README to be more clear
Update README to be more clear

This patch elaborates on fine-grained control of each service by listing
examples instead of using pseudocode - which could be confusing to
newcomers.

Change-Id: I9ba3c7b4460aa840e88c2c8c82aa70ba06c8302c

ajarr/devstack-plugin-ceph,openstack/devstack-plugin-ceph