Fix Typo in Documentation - "均衡工鞥呢" to "均衡功能"

[Bistutu]

In [specific file path, e.g., docs/usage.md], I noticed a typo in the phrase “负载均衡工鞥呢” (load balancing gong neng ne). The correct term should be “负载均衡功能” (load balancing function). This change improves the readability and professionalism of the documentation.

Impact:
This change is limited to the documentation text and does not affect any code functionality.