docs: correct casing for contextual tuples

[ewanharris]

Description

Corrects the readme docs casing for contextual tuples

References

openfga/sdk-generator#346

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

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.94%. Comparing base (a465788) to head (5057ded).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #94   +/-   ##
=======================================
  Coverage   83.94%   83.94%           
=======================================
  Files          18       18           
  Lines         922      922           
  Branches      210      161   -49     
=======================================
  Hits          774      774           
  Misses         71       71           
  Partials       77       77           

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