docs: fix image path in format guides

[Rukai-Jiang]

Summary

• correct the favicon example path in the Chinese format guide
• correct the same path in the English format guide
• fix the related English grammar

Problem

Both format guides are located in docs/contribution, so ./assets/favicon.png points to the nonexistent docs/contribution/assets directory. The asset is stored at docs/assets/favicon.png, making ../assets/favicon.png the correct relative path.

Validation

• verified that docs/assets/favicon.png exists
• scanned local Markdown links after the change
• ran git diff --check

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