"Table chq_sessions does not exist!" when following the quickstart guide

After following the steps described in https://docs.cachethq.io/docs/get-started-with-docker, I am greeted with the following errors:

cachet_1 | Attempting to connect to database ...
cachet_1 |
cachet_1 | Table chq_sessions does not exist! ...
cachet_1 | Initializing Cachet database ...
postgres_1 | ERROR: relation "chq_settings" does not exist at character 29
postgres_1 | STATEMENT: select "name", "value" from "chq_settings"

I am a newbie to docker, but I know how to read logs, and it seems something is wrong with the DB creation process. By looking at other similar issues I figured out I didn't create an app key (I just wanted to see how easy it was to have Cachet running quickly for a demo).

My problem is I have no idea how to create the app key (in a docker) and I couldn't find out how.

Is this completely out of the scope for the mentioned page? Is this prerequisite knowledge for using/running cachet?

Is there a way to automate this process and to make it easier for newbie users like me?