Updating an application within a Docker container via a web interface goes against the whole point of running Docker in the first place.
Lets say you update Sickbeard via the web interface. Then something happens and you need to regenerate your container. There goes your update, and your current database that was upgraded earlier is no longer compatible with the old version. Best case scenario SickBeard is offline, worst case scenario the database is corrupted and you have to now start from scratch.
Just Say No to git and updating via Web UI in Docker!