docs: note optional docker setup

docs/docker.md

@@ -0,0 +1,49 @@
+---
+summary: "Optional Docker-based setup and onboarding for Clawdis"
+read_when:
+  - You want a containerized gateway instead of local installs
+  - You are validating the Docker flow
+---
+
+# Docker (optional)
+
+Docker is **optional**. Use it only if you want a containerized gateway or to validate the Docker flow.
+
+## Quick start (recommended)
+
+From the repo root:
+
+```bash
+./docker-setup.sh
+```
+
+This script:
+- builds the image
+- runs the onboarding wizard
+- runs WhatsApp login
+- starts the gateway via Docker Compose
+
+It writes config/workspace on the host:
+- `~/.clawdis/`
+- `~/clawd`
+
+## Manual flow (compose)
+
+```bash
+docker build -t clawdis:local -f Dockerfile .
+docker compose run --rm clawdis-cli onboard
+docker compose run --rm clawdis-cli login
+docker compose up -d clawdis-gateway
+```
+
+## E2E smoke test (Docker)
+
+```bash
+scripts/e2e/onboard-docker.sh
+```
+
+## Notes
+
+- Gateway bind defaults to `lan` for container use.
+- Health check:
+  `docker compose exec clawdis-gateway node dist/index.js health --token "$CLAWDIS_GATEWAY_TOKEN"`