fix ckpt-converter readme (#96)

Author: odashi

ckpt_converter/README.md

@@ -10,6 +10,18 @@
 - Input checkpoints located at:
   - `TASK_DIR/checkpoints/iter_XXXXXXX` (7-digit zero-padded).
 
+How to install anappropriate venv (using uv):
+
+```shell
+mkdir cpuenv
+cd cpuenv
+uv python pin 3.13
+uv init
+uv venv
+uv pip install "torch==2.8.0+cpu" -i https://download.pytorch.org/whl/cpu
+uv pip install -r /path/to/ckpt_converter/requirements.txt
+```
+
 ### Usage
 ```bash
 bash scripts/ckpt_converter/convert_to_hf_cpu.sh \