Update docs with old README extract

Author: rsora

docs/getting-started.md

@@ -309,3 +309,41 @@ FTDebouncer@1.3.0 downloaded
 Installing FTDebouncer@1.3.0...
 Installed FTDebouncer@1.3.0
 ```
+
+
+Using the ``daemon`` mode and the gRPC interface
+------------------------------------------------
+
+Arduino CLI can be launched as a gRPC server via the `daemon` command.
+
+The [client_example] folder contains a sample client code that shows how to
+interact with the gRPC server. Available services and messages are detailed
+in the [gRPC reference] pages.
+
+
+To provide observability for the gRPC server activities besides logs,
+the `daemon` mode activates and exposes by default a [Prometheus](https://prometheus.io/)
+endpoint (http://localhost:9090/metrics) that can be fetched for
+telemetry data like:
+
+```text
+# TYPE daemon_compile counter
+daemon_compile{buildProperties="",exportFile="",fqbn="arduino:samd:mkr1000",installationID="ed6f1f22-1fbe-4b1f-84be-84d035b6369c",jobs="0",libraries="",preprocess="false",quiet="false",showProperties="false",sketchPath="5ff767c6fa5a91230f5cb4e267c889aa61489ab2c4f70f35f921f934c1462cb6",success="true",verbose="true",vidPid="",warnings=""} 1 1580385724726
+
+# TYPE daemon_board_list counter
+daemon_board_list{installationID="ed6f1f22-1fbe-4b1f-84be-84d035b6369c",success="true"} 1 1580385724833
+```
+
+The telemetry settings are exposed via the ``telemetry`` section
+in the CLI configuration:
+
+```yaml
+telemetry:
+  enabled: true
+  addr: :9090
+  pattern: /metrics
+```
+
+[client_example]: https://github.com/arduino/arduino-cli/blob/master/client_example
+[gRPC reference]: /rpc/commands
+[Prometheus]: https://prometheus.io/