Add missing configuration options to grpc readme (#10113)

instrumentation/grpc-1.6/README.md

@@ -1,5 +1,7 @@
 # Settings for the gRPC instrumentation
 
-| System property                                          | Type    | Default | Description                                         |
-| -------------------------------------------------------- | ------- | ------- | --------------------------------------------------- |
-| `otel.instrumentation.grpc.experimental-span-attributes` | Boolean | `false` | Enable the capture of experimental span attributes. |
+| System property                                             | Type    | Default | Description                                                                                                                                                    |
+|-------------------------------------------------------------|---------|---------|----------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `otel.instrumentation.grpc.experimental-span-attributes`    | Boolean | `false` | Enable the capture of experimental span attributes.                                                                                                            |
+| `otel.instrumentation.grpc.capture-metadata.client.request` | String  |         | A comma-separated list of request metadata keys. gRPC client instrumentation will capture metadata values corresponding to configured keys as span attributes. |
+| `otel.instrumentation.grpc.capture-metadata.server.request` | String  |         | A comma-separated list of request metadata keys. gRPC server instrumentation will capture metadata values corresponding to configured keys as span attributes. |