update readme for supporting RobustScanner

[tonytonglt]

Thank you for your contribution to the MindOCR repo.
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• You have read the Contributing Guidelines on pull requests
• Your code builds clean without any errors or warnings
• You are using approved terminology
• You have added unit tests

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Test Plan

(How should this PR be tested? Do you require special setup to run the test or repro the fixed bug?)

Related Issues and PRs

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[HaoyangLee]

https://github.com/mindspore-lab/mindocr/blob/main/docs/en/index.md#model-list
https://github.com/mindspore-lab/mindocr/blob/main/docs/en/mkdocs/modelzoo_training.md
这两处文档也添加robustscanner，包括中英文。

[tonytonglt]

https://github.com/mindspore-lab/mindocr/blob/main/docs/en/index.md#model-list https://github.com/mindspore-lab/mindocr/blob/main/docs/en/mkdocs/modelzoo_training.md 这两处文档也添加robustscanner，包括中英文。

已修改