train_agentfabric_llm_tool error

[xuhzyy]

In the 'modelscope-agent/docs/training_llms/train_agentfabric_llm_tool_use_cn.md' file, '--gradient_accumulation_steps $(expr 1 / $nproc_per_node) ' , 这个设置是否有问题（gradient_accumulation_steps =0），导致出现ZeroDivisionError: integer division or modulo by zero错误

[slin000111]

fixed, 参考#460