Improve documentation on Docker

[hizkifw]

There are some things to note when managing deployments using Docker, that isn't well-documented right now:

• The service runs as UID 1000, so bind-mount permissions need to be set correctly: chown -R 1000:1000 ./videos ./temp
• When using docker-compose, restarting the service will not update it. To update, use docker-compose pull and then docker-compose up -d