doc(api): add config and signal description

crates/synd_api/README.md

@@ -1,3 +1,49 @@
 # synd_api
 
 syndicationd graphql api server
+
+## OpenTelemetry
+
+synd-api is instrumented with OpenTelemetry.
+
+### Traces
+
+graphql request traces is exported
+
+### Metrics
+
+Following metrics are exported
+
+| Metrics               | Meter     | Description                          |
+| ---                   | ---       | ---                                  |
+| `http.server.request` | Counter   | http request traffic per status code |
+| `graphql.duration`    | Histogram | graphql latency                      |
+| `usecase`             | Counter   | usecase traffic per operation        |
+
+
+## Configurations
+
+| Flag                    | Description                                    | Example                    |
+| ---                     | ---                                            | ---                        |
+| `--addr`                | Server bind address                            | `0.0.0.0`                  |
+| `--port`                | Server bind port                               | `5959`                     |
+| `--timeout`             | Request timeout                                | `30s`                      |
+| `--body-limit-bytes`    | Request body limit                             | `2048`                     |
+| `--concurrency-limit`   | Request concurrency limit                      | `100`                      |
+| `--kvsd-host`           | Kvsd host                                      | `192.168.10.151`           |
+| `--kvsd-port`           | Kvsd port                                      | `7379`                     |
+| `--kvsd-username`       | Kvsd username                                  | `ferris`                   |
+| `--kvsd-password`       | Kvsd password                                  | `secret`                   |
+| `--tls-cert`            | Tls certificate path                           | `/path/to/certificate.pem` |
+| `--tls-key`             | Tls private key path                           | `/path/to/secret.pem`      | 
+| `--show-code-location`  | Show code location(foo.rs:10) in signals(logs) | `false`                    |
+| `--show-target`         | Show tracing target(module) ins signals(logs)  | `true`                     |
+| `--trace-sampler-ratio` | Trace sampler ratio                            | `1`                        |
+
+
+## Features
+
+| Feature                | Description                          | Default |
+| --                     | ---                                  | ---     |
+| `introspection`        | Enable graphql introspection         | false   |
+| `opentelemetry-stdout` | Enable opentelemetry stdout exporter | false   |