update custom parallel plan doc

Signed-off-by: Yuki Huang <[email protected]>

Author: yuki-97

docs/design-docs/fsdp2-parallel-plan.md

@@ -20,11 +20,11 @@ The Hugging Face tensor parallel plan is the default. It's available for most mo
 
 ## Custom Parallel Plan Example
 
-A custom parallel plan should be defined in a separate file, such as the example provided in `examples/custom_parallel.py`.
+A custom parallel plan should be defined in a separate file, such as the example provided in `examples/custom_parallel/custom_parallel.py`.
 
 To implement the custom parallel plan, either update the value of `custom_parallel_plan` in the `yaml` file directly, or pass the override via the command line. For example:
 
 ```bash
 uv run examples/run_grpo_math.py \
-    policy.dtensor_cfg.custom_parallel_plan=examples.custom_parallel.custom_parallel_plan
+    policy.dtensor_cfg.custom_parallel_plan=examples.custom_parallel.custom_parallel.custom_parallel_plan
 ```