docs: manhattan fallbackRouter options

[F-loat]

Description

Motivation and Context

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
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• My change requires a change to the documentation.
• I have updated the documentation accordingly.
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[x6-bot]

👋 @F-loat

💖 Thanks for opening this pull request! 💖

Please follow the contributing guidelines. And we use semantic commit messages to streamline the release process.

Examples of commit messages with semantic prefixes:

• fix: don't overwrite prevent_default if default wasn't prevented
• feat: add graph.scale() method
• docs: graph.getShortestPath is now available

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We get a lot of pull requests on this repo, so please be patient and we will get back to you as soon as we can.

[F-loat]

近距离下 orth 路由的表现比 er 差很多，需要自定义 fallbackRouter 来优化显示效果

[x6-bot]

👋 @F-loat

Congrats on merging your first pull request! 🎉🎉🎉