Document attachment scanning job command

#### Describe the task

Our cronjob in `check-file-status.yaml` uses a scary and complex bash command, it would be good to document what it does and what the arguments mean, so that a developer with no prior knowledge can understand what's happening

#### Acceptance Criteria

- [ ] first
- [ ] second
- [ ] third

#### Definition of Done

- [ ] first
- [ ] second
- [ ] third

#### Additional context

- Add any other context about the task here.
- Or here

Open check-file-status.yaml and inspect the cronjob command and its arguments. Document what the command does and what each argument means so a developer without prior knowledge can understand it; the generic acceptance criteria need to be clarified before completion can be verified.

Written by the indexing model from the issue text.