Add README with overview, doc links, structure, and status table

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

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+# video-setup
+
+A graph-based multi-peer video routing system written in C11. Nodes are media processes connected by typed transport edges; the graph carries video streams between sources, relays, and sinks with **priority** as a first-class property — so a low-latency monitoring feed and a high-quality archival feed can coexist on the same source.
+
+Designed to run on resource-constrained hardware (Raspberry Pi capturing raw MJPEG, forwarding over TCP) alongside more capable machines that handle processing, relay, display, and archival.
+
+## Documentation
+
+- [architecture.md](architecture.md) — system design: graph model, transport protocol, relay design, codec layer, discovery, multi-site plan, device resilience, X11 integration
+- [planning.md](planning.md) — module build order and current status
+- [conventions.md](conventions.md) — C code and project conventions
+
+### CLI Tools
+
+- [docs/cli/media_ctrl_cli.md](docs/cli/media_ctrl_cli.md) — media device and topology tool
+- [docs/cli/v4l2_ctrl_cli.md](docs/cli/v4l2_ctrl_cli.md) — V4L2 camera control tool
+
+## Structure
+
+```
+src/modules/     C modules, one directory each
+include/         public headers
+dev/cli/         CLI driver programs for each module
+dev/web/         development web UI (Node.js/Express, depends on protocol)
+docs/            documentation
+```
+
+## Status
+
+| Module | Status |
+|---|---|
+| `common` | done |
+| `media_ctrl` | done |
+| `v4l2_ctrl` | done |
+| `serial` | done |
+| `transport` | not started |
+| `protocol` | not started |
+| `frame_alloc` | not started |
+| `relay` | not started |
+| `ingest` | not started |
+| `archive` | not started |
+| `codec` | not started |
+| `xorg` | not started |
+| `web node` | not started |