docs(readme): correct invalid example in documentation

[azarboon]

Description

The original example is incorrect. The ID field also needs to be enclosed in double quotes, like "model_id", otherwise Strands CLI fails with the error strands: error: argument --model-config: invalid load_config value. This update corrects the example in the documentation.

Related Issues

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Documentation PR

[Link to related associated PR in the agent-docs repo]

Type of Change

• Documentation update

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Testing

[How have you tested the change?]

yes

• hatch fmt --linter
• hatch fmt --formatter
• hatch test --all

Checklist

• I have read the CONTRIBUTING document
• I have added tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature
• My changes generate no new warnings
• Any dependent changes have been merged and published

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