docs: fix grammar - add missing 'to' in model setup instructions

[haosenwang1018]

Fixes a grammar issue in the models documentation where the word 'to' was missing from the setup instructions.

Changed 'Add [Model] a config' to 'Add [Model] to a config' for all model entries in the documentation.

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Summary by cubic

Fixes missing "to" in model setup instructions by changing "Add [Model] a config" to "Add [Model] to a config". Applies to all model entries in docs/customize/models.mdx to improve clarity.

^{Written for commit 458e04a. Summary will update on new commits.}

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[cubic-dev-ai]

No issues found across 1 file

[RomneyDa]

@haosenwang1018 thanks for the contribution. This is not needed for now.