Docker description uses wrong setting file

In the description for docker, the following code is given to start the container:

`wget https://raw.githubusercontent.com/fsinfuhh/Bitpoll/master/bitpoll/settings_local.sample.py -O run/config/settings.py`

This downloads the settings file for the manual install. For docker the file under `docker_files/config/settings.py` is the correct file.