Add rationale for why this was built and how other solutions differ

[gene1wood]

Update the documentation

Enumerate other solutions for SSO for AWS and talk about how those solutions differ and why we built maws

[gene1wood]

Some info : https://docs.google.com/document/d/1o_fo28wY8MLPCcMhuRrtGUH47UYDHarUt8V5gwY-u6M/