Add FLOW to Multi-Agent Frameworks List

[KaeyoungLIAN]

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Hi,

This PR adds FLOW, a modular multi-agent framework powered by LLMs, to the Multi-agent section.

Key features of FLOW:

Organizes workflows as Activity-on-Vertex (AOV) graphs for parallel task execution.

Modular architecture allows local updates to subtasks without disrupting the overall pipeline.

Integrated validation mechanism reallocates or re-executes failed steps dynamically, improving robustness and adaptability.

We believe FLOW offers a valuable contribution to the open-source multi-agent ecosystem, especially for researchers and developers exploring scalable and fault-tolerant agent orchestration.