[feature] add some docs how to start with gunicorn

Hi, i am trying to run changedetection with gunicorn, but don't know how to pass datastore argument to the command line. played around, but i dont get it. at first we need gunicorn (i installed changedetection with a venv): `/opt/changedetection/bin/pip install gunicorn` some experiments, which fail: ``` /opt/changedetection/bin/gunicorn -w 1 -b 127.0.0.1:5000 --worker-class gevent 'changedetectionio.flask_app:changedetection_app(config={"datastore_path":"/opt/changedetection/data", data:["a"]}, datastore_o={"/opt/changedetection/data"})' /opt/changedetection/bin/gunicorn -w 1 -b 127.0.0.1:5000 --worker-class gevent 'changedetectionio.flask_app:app(datastore_o="/opt/changedetection/data")' /opt/changedetection/bin/gunicorn -w 1 -b 127.0.0.1:5000 --worker-class gevent changedetectionio.flask_app:app DATASTORE="/opt/changedetection/data" /opt/changedetection/bin/gunicorn -w 1 -b 127.0.0.1:5000 --worker-class gevent changedetectionio.flask_app:app DATASTORE="/opt/changedetection/data" /opt/changedetection/bin/gunicorn -w 1 -b 127.0.0.1:5000 --worker-class gevent changedetection /opt/changedetection/bin/gunicorn -w 1 -b 127.0.0.1:5000 --worker-class gevent 'changedetectionio.flask_app:changedetection_app(config=None, datastore_o="/opt/changedetection/data")' ``` before this, i used dev server, which warned about wsgi missing. so this works, but seems to be not charmant: `/opt/changedetection/bin/changedetection.io -d /opt/changedetection/data -h 127.0.0.1 -p 5000` are there any hints how to deal? searched the issues a while, did not find a good info