Add `ARC_TABLES_PORT` to the `CLI variables` section on the sandbox page

[TheWarBadger]

Hi,

ARC_TABLES_PORT isn't listed in the CLI variables section of the sandbox page (https://arc.codes/docs/en/reference/cli/sandbox) - although it is listed further down. It does however seem to be the only variable not listed in this section which is referenced on the page.

The CLI variables section also states Other variables will be ignored by Sandbox. which I took to mean that this was an exclusive list.

I've just lost a chunk of time to this - so I'd like to suggest updating the CLI variables section to include this variable. I'm happy to raise a PR to do this if that would be useful.

Thanks!