Update README.md

src/OpenTelemetry/README.md

@@ -251,7 +251,7 @@ together with following environmental variables:
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 | Environment variable       | Description                                        |
 | -------------------------- | -------------------------------------------------- |
-| `OTEL_RESOURCE_ATTRIBUTES` | Key-value pairs to be used as resource attributes. |
+| `OTEL_RESOURCE_ATTRIBUTES` | Key-value pairs to be used as resource attributes. See the [Resource SDK specification](https://github.com/open-telemetry/opentelemetry-specification/blob/v1.5.0/specification/resource/sdk.md#specifying-resource-information-via-an-environment-variable) for more details. |
 | `OTEL_SERVICE_NAME`        | Sets the value of the `service.name` resource attribute. If `service.name` is also provided in `OTEL_RESOURCE_ATTRIBUTES`, then `OTEL_SERVICE_NAME` takes precedence. |
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