Cargo "Smart filling mode" is not documented properly.

## Description
I have been lurking on the web(and here, of course) trying to get some information about Smart filling mode, but couldn't find one. 

## Wiki page (If applicable)
[Cargo management / Input Node](https://github.com/Slimefun/Slimefun4/wiki/Input-Node)

## Slimefun Version
LTS
