docs: icon-families vs icons

The font awesome pro icons I download include both an icons.json and an icon-families.json. The documentation for setup indicates:

```
Newer versions might have an icon-families.json. If this is the case, move its contents to path/to/your/font_awesome_flutter/lib/fonts/icons.json.
```
The intent is unclear.

This seems to indicate I should copy and paste the contents of icon-families.json into icons.json. It's not clear if that is the case or if you mean that the icon-families.json becomes the icons.json (for which a simple rename would work.) If you mean add the content of icon-families.json to icons.json, are you referring to adding it to the existing packages icons.json or to the newly downloaded icons.json (which would overwrite the one included in the font awesome flutter package.) The icon-families.json is massive--it's about 111 mb (not sure why that is with two styles and brands selected) so copying and pasting is not practical. I usually run out of memory on my M2 Max device so it would be helpful to clarify this step.