docs: add local verification commands

README.md

@@ -4,6 +4,8 @@ Minimal project skeleton for the OKX Codex Trader demo CLI.
 
 ## CLI usage
 
+Run these commands from the project virtual environment so `python` resolves to `.venv/bin/python`.
+
 ```bash
 python -m okx_codex_trader.cli fetch-history --symbol BTC-USDT-SWAP --bar 1H --limit 50
 python -m okx_codex_trader.cli backtest --symbol BTC-USDT-SWAP --bar 1H --limit 200 --leverage 2