Update the docker image entrypoint Pythonpath to use the top level media root folder.

Signed-off-by: Roberto Rosario <roberto.rosario.gonzalez@gmail.com>

docs/topics/docker.rst

@@ -275,3 +275,13 @@ These are:
 - mayan_broker - The broker volume, in this case RabbitMQ.
 - mayan_db - The database volume, in this case Postgres.
 - mayan_results - The celery result backend volume, in this case Redis.
+
+
+Nightly images
+==============
+The continious integration pipeline used for testing development builds also
+produces a resulting Docker image. These are build automatically and their
+stability is not guaranteed. They should never be used in production.
+If you want to try out the Docker images the development uses or want a sneak
+peek at the new features being worked on checkout the container registry at:
+https://gitlab.com/mayan-edms/mayan-edms/container_registry