FAQ/Charge Control C: add note about Modbus and ignore_echo

Signed-off-by: Moritz Barsnick <moritz.barsnick@chargebyte.com>

Author: barsnick

docs/source/troubleshooting.rst

@@ -133,6 +133,11 @@ EVerest already has a module which takes care of Modbus communication. Please ha
 `SerialCommHub <https://everest.github.io/nightly/_generated/modules/SerialCommHub.html>`_,
 and let your module interact with this module via the `serial_communication_hub` interface.
 
+.. note::
+   On Charge Control C's i.MX6, you need to suppress the echo on the RS-485 port. So, when
+   using the `SerialCommHub` module, its configuration option `ignore_echo` needs to be set
+   to `true`.
+
 .. _contact:
 
 .. include:: ../../includes/troubleshooting_contact.inc