Add rocotorc documentation when using scrontab

[DavidHuber-NOAA]

Description

Update the scrontab documentation to include information on the rocotorc file.

Resolves #3416

Type of change

• Maintenance (code refactor, clean-up, new CI test, etc.)

Change characteristics

• Is this a breaking change (a change in existing functionality)? NO
• Does this change require a documentation update? YES
• Does this change require an update to any of the following submodules? NO

How has this been tested?

Generated the documentation

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have documented my code, including function, input, and output descriptions
• My changes generate no new warnings
• New and existing tests pass with my changes
• This change is covered by an existing CI test or a new one has been added
• I have made corresponding changes to the system documentation if necessary

[EricSinsky-NOAA]

All changes look good to me. Thank you for adding documentation for this.

[aerorahul]

lgtm

[DavidHuber-NOAA]

I just a quick change to the path in the error message produced by the _check_rocotorc. It should be good to go now.