message: Add docker docs regarding file/logging
diff: @@ -160,6 +160,25 @@ for controlling access to an ``envoy`` socket from outside of the container.
  If you wish to run the container as the ``root`` user you can set ``ENVOY_UID`` to ``0``.
  +The ``envoy`` image sends application logs to ``/dev/stdout`` and ``/dev/stderr`` by default, and these
  +can be viewed in the container log.
  +
  +If you send application, admin or access logs to a file output, the ``envoy`` user will require the
  +necessary permissions to write to this file. This can be achieved by setting the ``ENVOY_UID`` and/or
  +by making the file writeable by the envoy user.
  +
  +For example, to mount a log folder from the host and make it writable, you can:
  +
  +.. substitution-code-block:: none
  +
  + $ mkdir logs
  + $ chown 777 logs
  + $ docker run -d -v `pwd`/logs:/var/log --name envoy -e ENVOY_UID=777 -p 9901:9901 -p 10000:10000 envoy:v1
  +
  +You can then configure ``envoy`` to log to files in ``/var/log``
  +
  +The default ``envoy`` ``uid`` and ``gid`` are ``101``.
  +
  Sandboxes
  ---------
  