Document uv local setup and ignore local runtime files

.gitignore

@@ -0,0 +1,4 @@
+.venv/
+__pycache__/
+*.py[cod]
+scratch/

README.md

@@ -13,3 +13,17 @@ which of PyBot's modules and files produced each reply. Pinned to commit `64eb2c
 
 `app.py` serves `site/` and `POST /api/chat` / `POST /api/trace`; `bot/bot-<sha12>.zip` holds the bot's source (`bot/**.py` only);
 `bot_runner.py` runs it in a fresh worker per request. Built by `build_pybot.py` in the swarmchat-release workspace.
+
+## Run locally
+
+Use Python 3.12 (required by the trace endpoint) on macOS or Linux:
+
+```sh
+uv venv --python 3.12 .venv
+source .venv/bin/activate
+uv pip install -r requirements.txt
+uvicorn app:app --host 127.0.0.1 --port 7860
+```
+
+Open http://127.0.0.1:7860. The health endpoint is `/health`.
+Keep local logs and temporary files in `scratch/`, which is ignored by Git.