feat(python-sdk): break WriteAuthorizationModelRequest into smaller pieces in README

[GMorris-professional]

Description

Breaking up the WriteAuthorizationModelRequest example in the README into smaller more understandable pieces.

References

openfga/python-sdk#29

Review Checklist

• I have clicked on "allow edits by maintainers".
• I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• The correct base branch is being used, if not main
• I have added tests to validate that the change in functionality is working as expected

[linux-foundation-easycla]

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