Improve documentation for pre-requisites

[juluriaj]

Currently information on pre-reqs is scattered between ‘choosing the deployment account’ and ‘pre-requisites’ and CloudFormation parameters pages.

Customers who wants to deploy this solution in Control Tower / Organizations are finding it difficult to deploy correctly. So it would help to clearly layout the instructions for CT deployment vs. Single account deployment.

Here are the pre-requisite resources in the order to be created for CT customers:

1. AWS Config Organization type aggregator must be created using this documentation: https://docs.aws.amazon.com/config/latest/developerguide/aggregated-create.html
2. Instructions clarifying required parameters like: CrossAccountDiscovery set to AWS_Organizations, Organization ID, Org type Config aggregator name
3. Setup delegate StackSets administration to the deployment account from Management account - https://docs.aws.amazon.com/solutions/latest/workload-discovery-on-aws/choosing-the-deployment-account.html
4. Register a Delegated Administrator for AWS Config in Management account - https://docs.aws.amazon.com/config/latest/developerguide/aggregated-register-delegated-administrator.html
5. Deploy CloudFormation stack in the deployment account