Update docs/opa/README.md
Wording improvement
# Open Policy Agent (Gatekeeper)
-As ASO is an operator defines a number of CDRs, this enables the use of OPA policies over the different objects being provisioned.
+Azure Service Operator defines a number of CDRs. OPA policies can be used to define constraints and policies for the different objects being provisioned.
For example you may want to limit the locations of the resources being created by ASO, this example is available in this repository with both the [template](./aso_allowed_locations-template.yaml) and the [constraint](./aso_allowed_locations-template.yaml)
