Readme explaining the new migration script moving to schemas
Update docs around making requests

- includes a live example that shows we need the signon api key, not the tokens that exist inside pp-deployment (are these now completely redundant?)
- Updates example json responses to show off the exciting new user listings
Merge pull request #180 from alphagov/document_users

Update docs around making requests
Merge pull request #179 from alphagov/docs-for-data-set-schema-change-script

Readme explaining the new migration script moving to schemas