Feedback: MOLT Fetch - missing documentation on userscript

Page: https://cockroachlabs.com/docs/molt/molt-fetch.html

## What is the reason for your feedback?

[X] Missing the information I need

[ ] Too complicated

[ ] Out of date

[ ] Something is broken

[ ] Other

## Additional details

The page says the following about the `--userscript` replication flag:
> The path to a configuration script, see userscript subcommand.

But the userscript subcommand is not documented on this page and is not listed in the section on subcommands.

Jira issue: DOC-13909