docs: expand README with usage, configuration, and metrics reference

README.md

@@ -1,7 +1,90 @@
 # DrayTek Exporter
 
-Prometheus exporter for DrayTek Vigor modems/routers
+[![CI](https://github.com/SuperQ/draytek_exporter/actions/workflows/ci.yml/badge.svg)](https://github.com/SuperQ/draytek_exporter/actions/workflows/ci.yml)
 
-# Currently supported devices
+Prometheus exporter for DrayTek Vigor modems/routers. Collects DSL line status and performance metrics via the DrayTek web API.
+
+## Supported Devices
 
 * DrayTek Vigor 167 (v5 firmware)
+
+## Installation
+
+### Pre-built binaries
+
+Download from the [releases page](https://github.com/SuperQ/draytek_exporter/releases).
+
+### Docker
+
+```sh
+docker run -e DRAYTEK_PASSWORD=yourpassword quay.io/superq/draytek-exporter --target=192.168.1.1
+```
+
+Multi-arch images are available for `amd64`, `armv7`, and `arm64`.
+
+### Building from source
+
+Requires Go 1.25+.
+
+```sh
+make build
+```
+
+## Usage
+
+```sh
+export DRAYTEK_PASSWORD=yourpassword
+./draytek_exporter --target=192.168.1.1
+```
+
+The exporter authenticates to the router's web interface, scrapes DSL status data, and exposes it as Prometheus metrics on `:9103/metrics`.
+
+### Flags
+
+| Flag | Default | Description |
+|------|---------|-------------|
+| `--target` | `192.168.1.1` | Router IP address or hostname |
+| `--username` | `monitor` | Username for router authentication |
+| `--password-env` | `DRAYTEK_PASSWORD` | Environment variable containing the password |
+| `--web.listen-address` | `:9103` | Address to listen on for HTTP requests |
+| `--web.telemetry-path` | `/metrics` | Path under which to expose metrics |
+
+### Router Setup
+
+Create a dedicated monitoring user on your DrayTek device (e.g. `monitor`) with read-only access. Avoid using the admin account.
+
+## Metrics
+
+All metrics use the `draytek_` prefix.
+
+| Metric | Type | Description |
+|--------|------|-------------|
+| `draytek_up` | Gauge | Whether the DSL link is up (1) or down (0) |
+| `draytek_info` | Gauge | Device info labels: `dsl_version`, `mode`, `profile` |
+| `draytek_downstream_actual_bps` | Gauge | Current downstream sync speed (bits/sec) |
+| `draytek_upstream_actual_bps` | Gauge | Current upstream sync speed (bits/sec) |
+| `draytek_downstream_attainable_bps` | Gauge | Maximum attainable downstream speed (bits/sec) |
+| `draytek_upstream_attainable_bps` | Gauge | Maximum attainable upstream speed (bits/sec) |
+| `draytek_downstream_snr_margin_db` | Gauge | Downstream signal-to-noise ratio margin (dB) |
+| `draytek_upstream_snr_margin_db` | Gauge | Upstream signal-to-noise ratio margin (dB) |
+| `draytek_downstream_actual_psd_db` | Gauge | Downstream power spectrum density (dB) |
+| `draytek_upstream_actual_psd_db` | Gauge | Upstream power spectrum density (dB) |
+| `draytek_downstream_interleave_depth` | Gauge | Downstream interleaving depth |
+| `draytek_upstream_interleave_depth` | Gauge | Upstream interleaving depth |
+| `draytek_{near,far}_end_attenuation_db` | Gauge | Line attenuation (dB) |
+| `draytek_{near,far}_end_bitswap_active` | Gauge | Whether bitswap is active |
+| `draytek_{near,far}_end_retx_active` | Gauge | Whether retransmission (G.INP) is active |
+| `draytek_{near,far}_end_crc_errors_total` | Counter | CRC error count |
+| `draytek_{near,far}_end_errored_seconds_total` | Counter | Errored seconds |
+| `draytek_{near,far}_end_severely_errored_seconds_total` | Counter | Severely errored seconds |
+| `draytek_{near,far}_end_unavailable_seconds_total` | Counter | Unavailable seconds |
+| `draytek_{near,far}_end_hec_errors_total` | Counter | Header error correction errors |
+| `draytek_{near,far}_end_los_failures_total` | Counter | Loss of Signal failures |
+| `draytek_{near,far}_end_lof_failures_total` | Counter | Loss of Frame failures |
+| `draytek_{near,far}_end_lpr_failures_total` | Counter | Loss of Power failures |
+| `draytek_{near,far}_end_lcd_failures_total` | Counter | Loss of Cell Delineation failures |
+| `draytek_{near,far}_end_reed_solomon_forward_error_corrections_total` | Counter | Reed-Solomon FEC corrections |
+
+## License
+
+Apache License 2.0. See [LICENSE](LICENSE).