boards/sarien: Update sarien documentation (Servo Micro + v4)

Signed-off-by: Ricardo Cañuelo <ricardo.canuelo@collabora.com>

content/boards/chromebooks/boards/sarien.md

@@ -15,19 +15,30 @@ such as the Celeron 4305U.
 
 The Dell Latitude 5400 Chromebook Enterprise has been flashed and tested
 with a [Servo Micro](../../01-debugging_interfaces) interface and a
-RTL8152-based USB-Ethernet adapter. Note that these devices don't
-support [CCD](../../02-ccd).
+RTL8152-based USB-Ethernet adapter, as well as with a combination of
+Servo Micro and Servo v4 as documented in [this
+page](https://chromium.googlesource.com/chromiumos/third_party/hdctools/+/HEAD/docs/servo_micro.md). Note
+that `sarien` Chromebooks don't support [CCD](../../02-ccd).
 
 #### Network connectivity
 
 An external USB-Ethernet dongle based on the Realtek RTL8152 can be used
 to provide Ethernet connectivity in Depthcharge. Alternatively, A Servo v4 can be
-used together with the Servo Micro to provide an Ethernet interface,
-although this hasn't been tested yet.
+used together with the Servo Micro to provide an Ethernet interface (see
+the [official
+docs](https://chromium.googlesource.com/chromiumos/third_party/hdctools/+/HEAD/docs/servo_micro.md)).
+
+Note that to be able to use the RTL8152 USB-Eth adapter, the kernel must
+be configured with `CONFIG_USB_RTL8152=y`.
 
 #### Known issues
 
-See [Common issues](../common_issues.md).
+After issuing a `cold_reset:on` command with `dut-control`, this device
+can't be turned on again with `cold_reset:off`. The recommended way to
+turn it off and on is with the `power_state:off` and `power_state:on`
+commands.
+
+See [Common issues](../common_issues.md) as well.
 
 ### Example kernel command line arguments