Docs: end-user guide; README brought up to date

docs/user-guide.md covers setup, the web page, sources and failover, the
Spotify developer app, AES67 output and SDP/SAP, PTP presets, network and
static IP, logging, firmware updates (OTA and USB), the player API,
troubleshooting and known limitations.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -1,10 +1,24 @@
 # aes67-ESP32-P4
 
-AES67 sender for the Waveshare ESP32-P4-ETH (PoE): Spotify Connect and HLS/m3u8 streams out as an AES67 multicast stream, PTP-locked, with a simple web UI for settings and SDP export.
+AES67 sender for the Waveshare ESP32-P4-ETH (PoE): Spotify Connect and HLS/m3u8 internet radio (with failover between them) go out as an AES67 multicast stream, locked to PTP. Everything is set up from a built-in web page, with SAP announcements and SDP export for receivers (tested with Riedel PTP).
 
-- `docs/aes67-core-base.md` — reusable AES67 core design (PTP, RTP, SDP/SAP, VLAN, syslog, web UI contract)
-- `docs/hardware-and-design-notes.md` — board details and project-specific design
-- `web/index.html` — web UI (served by the device)
-- `CLAUDE.md` — working rules and build order
+**Using it:** see the [user guide](docs/user-guide.md).
 
-Status: design complete, firmware not started. See the build order in CLAUDE.md.
+**Quick start:** power the board over PoE and open http://p4-aes67.local/. Pick a source and save. Then find "P4 AES67" via SAP on the receiver, or import the SDP from the page.
+
+## Building and flashing
+
+- ESP-IDF 5.5 or later, target `esp32p4`: `idf.py set-target esp32p4 && idf.py build`
+- cspot submodule: `git submodule update --init external/cspot && git -C external/cspot submodule update --init cspot/bell`
+- New board over USB: `tools/flash_board.py`
+- Update over the network: web page → Firmware, or `curl -f --data-binary @build/aes67_p4.bin -H 'Content-Type: application/octet-stream' http://p4-aes67.local/api/ota`
+
+Toolchain details and caveats (chip revision, Python packages for cspot) are in `CLAUDE.md`.
+
+## Documentation
+
+- `docs/user-guide.md`: setup, web page, sources, Spotify, AES67, PTP, network, updates, player API, troubleshooting
+- `docs/aes67-core-base.md`: reusable AES67 core design (PTP, RTP, SDP/SAP, syslog, web UI and API contract)
+- `docs/hardware-and-design-notes.md`: board details and project-specific design
+- `web/index.html`: the web page (served by the device)
+- `CLAUDE.md`: working rules, build order and status