Either update or deprecate MacPorts install

[dwreeves]

The docs currently contain:

Users on macOS can install `rich-click` via [MacPorts](https://ports.macports.org/port/py-rich-click/).

```bash
sudo port install py-rich-click
```

Going to the page, it's on 1.6.1, meaning the MacPorts install isn't being updated.

Either this should be updated or it should be deprecated.

It's a little tricky to use the rich-click CLI without a shared interpreter for the executable or script being targeted, so I don't know whether the MacPorts installation actually makes much sense.

@ewels wondering what you think.