document docker container usage

README.md

@@ -82,11 +82,22 @@ uvicorn app.main:app --reload --port 8000
 
 ## Docker
 
+Build and run the container image directly:
+
+```bash
+docker build -t registry.reversed.dev/registry/git-activity-merger:latest .
+docker run --rm -p 8000:8000 \
+  --env-file .env \
+  registry.reversed.dev/registry/git-activity-merger:latest
+```
+
+Or use Compose:
+
 ```bash
 docker compose up --build
 ```
 
-Container serves on port `8000` and mounts a named cache volume at `/app/cache`.
+Container serves on port `8000`. Compose mounts a named cache volume at `/app/cache`.
 
 ## Reverse Proxy Example (Nginx)