Emphasize billing setup in Ref Arch Organizations configuration section

[angelofenoglio]

Describe the Feature

Make sure that the Billing configuration step is properly emphasized in the initial AWS Organizations configuration section for the Leverage Reference Architecture. Particularly the Activate IAM User and Role Access to Billing Information item.
Also, add a guide or a reference to docs on how to create billing alarms to monitor costs. AWS Docs

Expected Behavior

The documentation should provide clear guidance on how to better view and monitor account and/or organization costs.

Use Case

Any user of the Leverage Reference Architecture.