docs: add info how to access serial port inside docker via rfc2217

On Windows/Mac the serial port cannot be access directly inside
docker container. This is already mentioned in the documentation.
This expands the documentation for steps which can be used to overcome
this limitation by using remote serial port access via telnet protocol.

Closes https://github.com/espressif/esp-idf/issues/10617

Signed-off-by: Frantisek Hrbata <frantisek.hrbata@espressif.com>

docs/en/api-guides/tools/idf-docker-image.rst

@@ -60,7 +60,7 @@ The above command explained:
 - ``espressif/idf``: uses Docker image ``espressif/idf`` with tag ``latest`` (implicitly added by Docker when no tag is specified)
 - ``idf.py build``: runs this command inside the container
 
-To build with a specific docker image tag, specify it as ``espressif/idf:TAG``, for example::
+To build with a specific Docker image tag, specify it as ``espressif/idf:TAG``, for example::
 
     docker run --rm -v $PWD:/project -w /project espressif/idf:release-v4.4 idf.py build
 
@@ -81,7 +81,25 @@ Then inside the container, use ``idf.py`` as usual::
 
 .. note::
 
-    Commands which communicate with the development board, such as ``idf.py flash`` and ``idf.py monitor`` will not work in the container unless the serial port is passed through into the container. However currently this is not possible with Docker for Windows (https://github.com/docker/for-win/issues/1018) and Docker for Mac (https://github.com/docker/for-mac/issues/900).
+    Commands which communicate with the development board, such as ``idf.py flash`` and ``idf.py monitor`` will not work in the container unless the serial port is passed through into the container. This can be done with Docker for Linux with the `device option`_. However currently this is not possible with Docker for Windows (https://github.com/docker/for-win/issues/1018) and Docker for Mac (https://github.com/docker/for-mac/issues/900). This limitation may be overcome by using `remote serial ports`_. An example how to do this can be found in the following `using remote serial port`_ section.
+
+
+.. _using remote serial port:
+
+Using remote serial port
+~~~~~~~~~~~~~~~~~~~~~~~~
+The `RFC2217`_ (Telnet) protocol can be used to remotely connect to a serial port. For more information please see the `remote serial ports`_ documentation in the esptool project. This method can also be used to access the serial port inside a Docker container if it cannot be accessed directly. Following is an example how to use the flash command from within a Docker container.
+
+On host start ``esp_rfc2217_server``. It is available as a one-file bundled executable created by pyinstaller and it can be downloaded from the `esptool releases`_ page in a zip archive along with other esptool utilities::
+
+    esp_rfc2217_server -v -p 4000 COM3
+
+Now the device attached to the host can be flashed from inside a Docker container by using::
+
+    docker run --rm -v <host_path>:/<container_path> -w /<container_path> espressif/idf idf.py --port rfc2217://host.docker.internal:4000?ign_set_control flash
+
+Please make sure that ``<host_path>`` is properly set to your project path on the host and ``<container_path>`` is set as a working directory inside the container with the ``-w`` option. The ``host.docker.internal`` is a special Docker DNS name to access the host. This can be replaced with host IP if necessary.
+
 
 Building custom images
 ======================
@@ -101,3 +119,8 @@ To use these arguments, pass them via the ``--build-arg`` command line option. F
         --build-arg IDF_CLONE_SHALLOW=1 \
         --build-arg IDF_INSTALL_TARGETS=esp32c3 \
         tools/docker
+
+.. _remote serial ports: https://docs.espressif.com/projects/esptool/en/latest/esptool/remote-serial-ports.html
+.. _RFC2217: http://www.ietf.org/rfc/rfc2217.txt
+.. _esptool releases: https://github.com/espressif/esptool/releases
+.. _device option: https://docs.docker.com/engine/reference/run/#runtime-privilege-and-linux-capabilities